Indulge in Joanna Gaines’ Iconic Frosted Peanut Butter Brownies: The Perfect Loaf Pan Recipe (Lucy’s Brownies Reimagined)

There’s something uniquely comforting about a classic homemade brownie, and when you combine it with the creamy goodness of peanut butter and a luscious chocolate frosting, you create an irresistible treat. Today, I finally had the pleasure of trying my hand at a recipe that goes by many names: Lucy’s Peanut Butter Brownies, Magnolia Brownies, or even Joanna Gaines’s beloved Brownies. This dessert isn’t just a simple baked good; it’s a testament to timeless flavors, a recipe cherished and passed down through generations, leaving a delicious legacy in its wake. Its enduring popularity is evident in its appearance in the 1992 Southern Living Annual, where it was known as Frosted Peanut Butter Brownies. This rich history hints at a recipe that has stood the test of time, evolving slightly but always delivering on its promise of a truly decadent experience. At its heart, it’s a beautifully basic cocoa brownie, elevated by a generous layer of smooth peanut butter, all crowned with a very sweet, cocoa-based frosting that brings everything together in perfect harmony. It’s a treat that promises to satisfy any sweet tooth, blending the deep richness of chocolate with the nutty comfort of peanut butter in every single bite.

Jump to Recipe

The Convenient and Easy Loaf Pan Version of These Beloved Brownies

While the allure of baking the original, large-batch version of these celebrated brownies is strong, it’s typically designed for a 13×9 inch pan, yielding a substantial amount that might be too much for smaller households or to simply enjoy without overindulging. My adaptation scales this classic recipe down beautifully to fit a standard loaf pan, making it incredibly manageable. This scaled-down version produces approximately 8 rich brownies, or perhaps 16 if you prefer smaller, more modest squares of this intensely decadent treat. Let’s be honest, these brownies are exceptionally rich and satisfying, so a smaller batch often means less waste and a perfect portion for sharing (or not!).

Beyond the convenient sizing, this recipe offers another significant advantage: its sheer simplicity. It’s remarkably easy to make and requires only a handful of common pantry ingredients, making it accessible even for novice bakers. You won’t need any fancy equipment or exotic components. A significant portion of the preparation involves passive cooling and chill time, which means less active work for you and more anticipation for the delicious outcome. This extended chilling also contributes to the brownies’ optimal texture and makes the layering process much smoother. So, even if you find yourself missing a key ingredient like marshmallows, a quick trip to the store is all you’ll need to complete this delightful dessert.

Essential Tips for Perfect Loaf Pan Lucy’s Peanut Butter Brownies

Crafting the perfect batch of these Frosted Peanut Butter Brownies in a loaf pan involves a few key considerations that can elevate your baking experience and ensure a fantastic result. While the recipe itself is straightforward, paying attention to these details can make all the difference. I won’t delve into an ingredient-by-ingredient breakdown, as most are self-explanatory, but here are some crucial tips to keep in mind:

• **Choosing the Right Loaf Pan:** I personally used an 8 ½ by 4 ½ inch loaf pan for this scaled-down recipe, which I highly recommend. This size provides a good depth for the brownies, resulting in that wonderfully fudgy interior and a substantial base layer. If you opt for a larger 9×5 inch pan, be aware that the surface area will be wider, which means your brownies will likely bake faster and yield a thinner bottom layer. Keep a close eye on the baking time if you deviate from the recommended pan size to avoid overbaking.
• **Mastering the Brownie Batter Method:** The original recipes from Lucy, Joanna Gaines, and Southern Living traditionally call for beating the sugar and flour together first, then incorporating a cocoa and butter mixture, and finally adding the eggs. However, to simplify the process and achieve an even fudgier texture—without any risk of overbeating—I’ve adopted a slightly different approach. I combine the sugar directly with the melted cocoa and butter mixture, then hand-beat in the egg, followed by stirring in the salt, vanilla, and flour. This method is a tried-and-true technique for yielding incredibly dense, rich, and fudgy brownies every time.
• **Peanut Butter Layer – Less Can Be More:** You might notice a discrepancy in the original recipes: the Southern Living version suggests 12 oz of peanut butter, while Lucy’s calls for a more generous 16 oz. For my quarter-batch loaf pan recipe, I found that around 3 ½ oz (½ cup) was just right. The critical lesson I learned here is that more peanut butter isn’t always better. An excessive amount can easily overpower the delicate balance of the other components, especially the rich chocolate brownie and the sweet marshmallow frosting. Aim for a distinct but harmonious peanut butter presence.
• **The Magic of Marshmallows in Frosting:** Don’t underestimate the power of marshmallows in this frosting! You only need about 2 ½ large marshmallows (or approximately 25 small ones) to make a significant difference. These little additions are crucial for achieving that characteristic soft, slightly chewy, and perfectly smooth texture that sets this frosting apart. They contribute to the overall richness and mouthfeel in a way that powdered sugar alone cannot.
• **Gradual Powdered Sugar for Frosting Perfection:** This frosting is known for being quite stiff and sweet, so precise control over the powdered sugar is important. Add the sifted powdered sugar gradually, mixing thoroughly after each addition. Depending on your desired consistency and sweetness level, you may find that you need slightly less than the recipe calls for to achieve a softer, more spreadable frosting. Always taste as you go!
• **Update: Frosting Ingredient Order Refinement:** Based on further experimentation, I’ve modified the order of ingredients for the frosting. For the smoothest and most consistent result, begin by melting the marshmallows together with the butter first. Once the marshmallows are nearly fully melted and very soft, then proceed to add the cocoa powder and milk, followed by the gradual incorporation of the powdered sugar. This ensures a uniform melt and a velvety frosting texture.

Explore More Peanut Butter & Marshmallow Brownie Combinations

If you’re a fan of the delightful combination of peanut butter, marshmallows, and chocolate brownies, there’s a whole world of variations to explore beyond this classic Lucy’s recipe. Each offers a unique twist on this beloved flavor profile, providing different textures and levels of complexity. Here are a few other fantastic recipes that celebrate these indulgent ingredients:

• Frosted Marshmallow Brownies — This old favorite from “Baking Blonde” focuses purely on the ethereal marshmallow frosting, creating a chewy, sweet topping that perfectly complements a rich brownie base.
• Frosted Fudge Brownies — While this recipe skips the marshmallows, it remains a timeless favorite for its intensely fudgy brownie and gloriously smooth chocolate frosting, delivering pure chocolate decadence.
• Cape Town Brownies — For those who love an added textural surprise, these brownies feature charming little marshmallows folded directly into the batter, ensuring every bite is wonderfully soft and chewy.
• Marshmallow Krispie Topped Brownie — I won’t lie, these are arguably even better! The addition of a crunchy, sweet Rice Krispie topping with marshmallow and peanut butter creates an incredible textural contrast that takes these brownies to the next level. They require just a little more effort and you’ll need to have some rice cereal on hand, but the reward is immense.
• Dorie Greenspan’s Peanut Butter Brownies — A truly unique take, Dorie Greenspan’s version features brownies made with a rich chocolate base and a peanut butter layer that’s more akin to a Reese’s filling than straight peanut butter. They’re beautifully finished with an easy ganache, offering a sophisticated and distinct flavor profile. This is another one I need to scale down for a loaf pan!

Whether you’re looking for a simple, classic brownie with a nutty twist, or eager to explore variations with added crunch and chewiness, these recipes offer a diverse range of options for every brownie enthusiast. Enjoy the journey through these delightful dessert combinations!

Recipe

Frosted Peanut Butter Brownies in a Loaf Pan

Anna

These delightful Frosted Peanut Butter Brownies, scaled to perfection for a loaf pan, feature a rich, fudgy cocoa brownie base, generously topped with a creamy layer of peanut butter and finished with a sweet, marshmallow-infused chocolate frosting.

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Prep Time 10 minutes mins

Cook Time 20 minutes mins

Total Time 38 minutes mins

Course Dessert

Cuisine American

Servings 8

Ingredients

 

For the Brownies

• 4 tablespoons unsalted butter (salted butter is likely okay too, 56 grams)
• 1 ½ tablespoons unsweetened cocoa powder (about 8 grams)
• ½ cup granulated sugar (100 grams)
• 1 large egg
• ¼ teaspoon vanilla extract
• ⅛ teaspoon salt
• 6 tablespoons all-purpose flour (equivalent to ¼ cup plus 2 tablespoons, 48 grams)
• ¼ cup semisweet chocolate chips (optional, but highly recommended for extra richness)

For the Peanut Butter Layer

• ½ cup creamy or crunchy peanut butter (choose your preference!)

For the Marshmallow Frosting

• 2 tablespoons unsalted or salted butter (I used unsalted, 28 grams)
• 2 ½ large marshmallows (or 25 small marshmallows)
• 1 tablespoon unsweetened cocoa powder (5 grams)
• 1 ½ tablespoons whole milk
• 1 cup sifted powdered sugar (you can use as little as ⅔ cup for a softer, less sweet frosting, 100 grams)

Instructions

 

• Preheat your oven to 325 degrees F (160 degrees C). Prepare an 8 ½ by 4 ½ inch loaf pan by lining it with a double layer of foil, ensuring enough overhang on the sides to easily lift the brownies out later. Grease the bottom only of the foil-lined pan.
• In a 1 ½ to 2 quart saucepan placed over medium-low heat, melt the unsalted butter until fully liquefied. Once melted, add the unsweetened cocoa powder and stir continuously until the mixture is smooth and well combined. Remove the saucepan from the heat, then immediately add the granulated sugar, stirring just until it begins to take on a glossy sheen. Allow this mixture to cool slightly (it should still be warm but not hot enough to scramble an egg). Beat in one cold large egg until it is fully blended and the mixture is cohesive. Finally, stir in the salt and all-purpose flour until just combined. Let the batter cool further for about 10 minutes.
• Before adding the chocolate chips, ensure the brownie mixture has cooled sufficiently so that it won’t melt the chips instantly. Once cooled to a suitable temperature, gently fold in the semisweet chocolate chips (if using).
• Scrape all of the prepared brownie batter into your foil-lined and greased loaf pan. Use a spatula to spread the batter evenly across the bottom of the pan, ensuring a uniform layer.
• Bake the brownie in the preheated 325 degrees F (160 degrees C) oven for 18 to 20 minutes. The brownies are done when an internal temperature probe reads around 200 degrees F. For optimal fudginess, it’s generally better to slightly underbake these brownies than to overbake them, so be vigilant and avoid extending the baking time unnecessarily.
• Once baked, remove the warm brownies from the oven. For the peanut butter layer, microwave the creamy or crunchy peanut butter for about 30 seconds, or until it’s slightly softened and easily spreadable. Carefully spread this warm peanut butter evenly over the top of the still-warm brownies. Allow the brownies to cool at room temperature for a few minutes, then transfer the pan to the refrigerator and chill for approximately 20 minutes, or until the peanut butter layer has firmed up somewhat.
• While the brownies are chilling, prepare your marshmallow frosting ingredients. Make sure your powdered sugar is already sifted and weighed out, as it will need to be added quickly once the other frosting ingredients are melted.
• Clean out the saucepan you used earlier for the brownie batter. In the clean saucepan, melt the butter and marshmallows together over low to medium-low heat, stirring frequently. Once the marshmallows are very soft and almost fully melted, add the cocoa powder and whole milk. Stir until the mixture is completely smooth and homogeneous. Gradually add half of the sifted powdered sugar and begin stirring. Remove the saucepan from the heat and continue to stir vigorously until the frosting is smooth, then gradually incorporate the remaining powdered sugar until you reach your desired consistency.
• Continue stirring the frosting until it is perfectly smooth and has a beautiful shiny appearance. Immediately pour this warm frosting mixture over the chilled peanut butter layer on your brownies. To set the frosting, place the loaf pan in the freezer for about 20 to 30 minutes, or simply let it sit at room temperature for a longer period until fully set. Once firm, use the foil overhangs to carefully lift the entire brownie slab from the loaf pan. Trim any uneven edges for a clean presentation (and enjoy those delicious scraps yourself!), then cut the remaining brownies into 8 neat squares. Serve and enjoy!

Notes

It’s interesting to note that the version of this recipe found in the 1992 Southern Living Annual explicitly calls for either butter or margarine. This inclusion of “or margarine” often serves as a historical clue that the original recipe was likely developed with salted butter in mind. Therefore, if you wish to experiment with a slightly different flavor profile, using salted butter in conjunction with the ⅛ teaspoon of added salt should work beautifully and maintain the intended balance of flavors. Trust your taste buds and experiment with confidence!

Keyword Joanna Gaines, Lucy’s Brownies, Magnolia Brownies, Peanut Butter Brownies, Frosted Brownies, Loaf Pan Dessert, Homemade Brownies, Chocolate Peanut Butter

Tried this recipe?Let us know how it was!

There you have it – the celebrated Lucy’s Peanut Butter Brownies, also famously known as Joanna Gaines’ Magnolia Brownies or the Frosted Peanut Butter Brownies from Southern Living, expertly scaled down for a convenient loaf pan. This recipe truly embodies the joy of home baking, offering a rich, comforting, and utterly decadent dessert that’s perfect for any occasion, big or small. The deep chocolate brownie, the luscious peanut butter layer, and the sweet marshmallow frosting create a symphony of flavors and textures that are simply irresistible. Whether you’re making them for a quiet evening at home, a small gathering, or simply to satisfy a craving, these brownies are sure to become a cherished addition to your recipe collection. Don’t hesitate to dive in and experience the magic of these timeless frosted peanut butter brownies!