Monster Cookie Fudgy Brownies: The Ultimate Mashup Dessert
Satisfy two cravings at once with these Monster Cookie Fudgy Brownies, a rich dessert that merges classic fudgy brownies with vibrant monster cookie dough.
This recipe combines a simple brownie batter with a quick, no-chill monster cookie dough, baking in approximately 30-35 minutes for a perfectly set treat.
Ideal for potlucks, celebrations, or as a decadent after-dinner dessert, these brownies offer a delightful blend of textures and flavors.
The fudgy brownie base ensures a dense, chocolatey foundation, while the monster cookie elements—oats, peanut butter, M&M’s, and chocolate chips—add contrasting chewiness and vibrant color. Achieve optimal fudginess by using good quality cocoa powder and not overbaking. The simple layering technique makes this an approachable recipe for all skill levels. These brownies hold well at room temperature, making them excellent for sharing.
Monster Cookie Fudgy Brownies
Monster Cookie Fudgy Brownies combine dense chocolate brownies with chewy peanut butter oatmeal cookie dough, M&M’s, and chocolate chips.
Equipment
- 8×8 inch (20×20 cm) baking pan
- Parchment paper
- Large mixing bowls (2)
- Medium heat-proof bowl
- Small mixing bowls (2)
- Whisk
- Rubber spatula
- Electric mixer (handheld or stand mixer with paddle attachment)
- Measuring cups and spoons
- Offset spatula or spoon
- Sharp knife or skewer
- Wire cooling rack
Ingredients
- ½ cup (113g) unsalted butter, cut into cubes
- 4 oz (113g) unsweetened chocolate, chopped
- 1½ cups (300g) granulated sugar
- 3 large eggs
- 1 teaspoon (5ml) vanilla extract
- ¾ cup (90g) all-purpose flour
- ¼ cup (24g) unsweetened cocoa powder
- ½ teaspoon (2.5g) salt
- ¼ cup (56g) unsalted butter, softened
- ½ cup (128g) creamy peanut butter
- ¼ cup (50g) granulated sugar
- ¼ cup (50g) packed light brown sugar
- 1 large egg yolk
- ½ teaspoon (2.5ml) vanilla extract
- ½ cup (45g) old-fashioned rolled oats
- ¼ cup (30g) all-purpose flour
- ¼ teaspoon (1.2g) baking soda
- ½ cup (85g) M&M’s chocolate candies, plus 2 tablespoons (28g) for topping
- ½ cup (85g) semi-sweet chocolate chips, plus 2 tablespoons (28g) for topping
For the Fudgy Brownie Base:
For the Monster Cookie Dough Swirl:
Instructions
- Preheat oven to 350°F (175°C). Line an 8×8 inch (20×20 cm) baking pan with parchment paper, allowing overhang for handles. Lightly grease parchment paper with cooking spray.
- Combine ½ cup (113g) cubed unsalted butter and 4 oz (113g) chopped unsweetened chocolate in a medium heat-proof bowl. Melt over a double boiler or in a microwave (30-second intervals, stirring vigorously), until smooth and melted (1-2 minutes). Set aside to cool for 5-7 minutes.
- Whisk 1½ cups (300g) granulated sugar, 3 large eggs, and 1 teaspoon (5ml) vanilla extract in a large mixing bowl for 2 minutes, until pale yellow, slightly thickened, and frothy.
- Gradually pour cooled chocolate mixture into egg-sugar mixture, whisking continuously. Whisk until batter is smooth, glossy, and no streaks remain.
- Whisk ¾ cup (90g) all-purpose flour, ¼ cup (24g) unsweetened cocoa powder, and ½ teaspoon (2.5g) salt in a small bowl until combined. Gently fold dry ingredients into wet ingredients with a rubber spatula until just combined, with no dry flour pockets.
- Cream ¼ cup (56g) softened unsalted butter, ½ cup (128g) creamy peanut butter, ¼ cup (50g) granulated sugar, and ¼ cup (50g) packed light brown sugar in a medium bowl with an electric mixer on medium speed for 2-3 minutes, until light and fluffy.
- Beat 1 large egg yolk and ½ teaspoon (2.5ml) vanilla extract into the creamed mixture for 30 seconds, until fully incorporated. Scrape down bowl sides with a spatula.
- Whisk ½ cup (45g) old-fashioned rolled oats, ¼ cup (30g) all-purpose flour, and ¼ teaspoon (1.2g) baking soda in a small bowl. Gradually add this dry mixture to the wet cookie dough, mixing on low speed with an electric mixer or by hand until just combined, with no dry streaks.
- Gently fold ½ cup (85g) M&M’s chocolate candies and ½ cup (85g) semi-sweet chocolate chips into the cookie dough with a spatula until evenly distributed.
- Pour two-thirds of brownie batter into the parchment-lined pan. Spread evenly with an offset spatula or spoon to create a base layer. Dollop 1-2 tablespoon spoonfuls of monster cookie dough randomly over the brownie layer, leaving gaps.
- Dollop remaining one-third brownie batter over and around cookie dough portions. Gently swirl batters together a few times with a knife or skewer to marble, avoiding over-swirling. Sprinkle reserved 2 tablespoons (28g) M&M’s and 2 tablespoons (28g) chocolate chips evenly over the top.
- Bake for 30-35 minutes at 350°F (175°C). Brownies are done when a wooden skewer inserted into the center (avoiding cookie dough) comes out with moist crumbs, not wet batter. Edges appear set and slightly puffed.
- Remove pan from oven. Transfer to a wire cooling rack; cool completely at room temperature for 2-3 hours. For fudgiest texture and clean cuts, chill cooled brownies in the refrigerator for at least 1 hour before slicing.
- Once cooled and chilled, lift brownie slab from pan using parchment overhang. Transfer to a cutting board. Cut into 16 even squares. Serve at room temperature or slightly chilled. Store leftovers in an airtight container: room temperature for up to 3 days, or refrigerator for up to 5 days.
Notes
- Do not overbake. Brownies should appear slightly underbaked and moist in the center upon removal; they will set as they cool.
- Use room temperature unsalted butter for cookie dough. This ensures proper creaming with sugars and peanut butter for a smooth, even dough.
- For clean cuts, chill cooled brownies in the refrigerator for 30-60 minutes before slicing. Use a large, sharp knife. Wipe blade clean with a damp cloth after each cut to prevent sticking.
- Customize cookie dough by substituting or adding inclusions: chopped peanuts, peanut butter chips, or white chocolate chips. Maintain total mix-in quantity around 1 cup (170g).
Pro Tips for Perfect Monster Cookie Fudgy Brownies
Ingredient Tips
- Melted Butter & Chocolate Temperature:Melt 1 cup (226g) unsalted butter with 4 oz (113g) unsweetened chocolate until the mixture reaches 110-120°F (43-49°C). This specific temperature range prevents the eggs from scrambling when added later, ensuring a smooth, emulsified batter.
- Egg Temperature:Use 3 large eggs at room temperature (around 70°F / 21°C). This helps them incorporate seamlessly into the batter, promoting a stable emulsion and a uniform, fudgy crumb without any curdling.
- Flour Measurement:Measure 1 cup (120g) all-purpose flour using a kitchen scale for precision, or spoon and level it. Over-measuring by even 2 tablespoons can lead to a dry, cakey brownie texture instead of rich fudginess.
- Peanut Butter Choice:Opt for 1/2 cup (128g) creamy, no-stir peanut butter (like Jif or Skippy), rather than natural peanut butter. Its consistent texture ensures beautiful, distinct swirls that don’t separate or become greasy during baking.
- Oat Type:Incorporate 1/2 cup (40g) quick-cooking oats into the batter. These smaller, thinner oats blend better and contribute to a soft, chewy cookie-like texture without making the brownies dense or tough, unlike old-fashioned oats.
- Chocolate Chip & M&M’s Coating:Toss 1.5 cups (250g) of chocolate chips and M&M’s with 1 teaspoon of all-purpose flour before folding them into the batter. This light coating creates friction, preventing them from sinking to the bottom during baking and ensuring even distribution.
Technique Tips
- Sugar Whisking Duration:Once sugars are added to the cooled butter/chocolate mixture, whisk vigorously for a full 2 minutes, or until the mixture becomes noticeably glossy and slightly thickened. This crucial step fully dissolves sugar crystals, leading to that characteristic shiny, crinkly top.
- Egg Incorporation:Add the 3 room temperature eggs one at a time, beating for 30 seconds after each addition. This ensures each egg is fully emulsified, creating a stable batter that prevents the brownies from becoming cakey and promotes a dense, fudgy interior.
- Dry Ingredients Folding:Fold in the dry ingredients (flour, cocoa, baking powder, salt) for a maximum of 15-20 seconds, or until just combined and no streaks of flour are visible. Overmixing develops gluten, resulting in tough, dry brownies instead of soft, fudgy ones.
- Peanut Butter Swirl Technique:Dollop the 1/2 cup (128g) slightly warmed peanut butter onto the brownie batter in 6-8 distinct spots. Use a skewer or butter knife to gently swirl it through the top 1/2 inch of batter 2-3 times, creating clear, marbled patterns without fully mixing.
- Baking Doneness Check:Bake at 350°F (175°C) for 28-32 minutes in a 9×13-inch metal pan. A wooden skewer inserted 2 inches from the edge should come out with moist crumbs attached, while the center may still look slightly soft. The edges should appear set and just beginning to pull away.
- Cooling Time:Allow the brownies to cool completely in the pan on a wire rack for a minimum of 2 hours, or ideally 4 hours. Cutting them while warm will result in crumbly, messy pieces that stick to the knife; proper cooling allows them to set into firm, clean squares.
Monster Cookie Brownie Variations & Substitutions
Essential Substitutions
- Unsalted Butter:
- (Oil creates a slightly denser, chewier brownie with less dairy richness. Plant-based butter maintains similar texture but may offer a subtle flavor difference.)
- Large Eggs:
- (Flax eggs add a nutty undertone, making brownies denser and chewier. Commercial replacers generally yield closer texture, though some may be slightly cake-like.)
- Granulated Sugar:
- (Brown sugar adds moisture and caramel notes, resulting in softer, chewier brownies. Coconut sugar lends a subtle caramel sweetness, less intense, maintaining similar moisture and texture.)
- All-Purpose Flour:
- (GF blend gives a similar crumb without gluten, possibly more delicate. Whole wheat pastry flour adds a mild nutty flavor, fiber, resulting in slightly denser, heartier crumb.)
- Creamy Peanut Butter:
- (Almond butter offers a milder nutty flavor. Sunflower seed butter provides a distinct toasted, earthy flavor and is nut-free; can react with leavening to create a harmless greenish tint post-baking.)
Dietary Variations
- Gluten-Free:
- Replace all-purpose flour with a 1:1 gluten-free all-purpose baking flour blend (ensure xanthan gum). No other changes needed.
- Dairy-Free/Vegan:
- Replace butter with 1:1 plant-based butter sticks. For vegan, replace each large egg with 1 flax egg. Ensure all chocolate chips and M&M’s are dairy-free/vegan.
- Nut-Free:
- Substitute peanut butter with 1:1 sunflower seed butter. Ensure all chocolate chips and candy mix-ins are certified nut-free.
- Reduced Sugar:
- Reduce total sugar by up to 1/4 cup, or substitute 1/2 of the sugar with a 1:1 granular erythritol-based sweetener. Reducing sugar yields a less sweet, potentially denser brownie; erythritol may impart a cooling sensation.
Flavor Variations
- Espresso Boost:
- Stir 1-2 teaspoons of instant espresso powder into the melted butter and cocoa mixture. Deepens chocolate flavor significantly without strong coffee taste.
- Dark Chocolate Intensity:
- Replace cocoa powder with 1:1 Dutch-processed dark cocoa powder. Swap semi-sweet chocolate chips for 1:1 dark chocolate chips (60-70% cacao). Results in a richer, less sweet, intensely chocolatey brownie.
- Salty Pretzel Crunch:
- Add 1 cup of roughly crushed pretzels along with chocolate chips, M&M’s, and oats. Adds a delightful salty crunch, balancing sweetness and chewiness.
- Swirled Peanut Butter:
- Dollop 1/2 cup warmed creamy peanut butter over half the batter, cover with remaining, then swirl gently. Creates beautiful ribbons and intensifies nutty flavor.
- White Chocolate Macadamia:
- Replace milk chocolate chips with 1:1 white chocolate chips and omit M&M’s. Add 1/2 cup chopped macadamia nuts with oats. Provides a rich, buttery, tropical twist.