Step 1: Preheat the Oven - Start by preheating your oven to 350°F (175°C). This ensures your brownies bake evenly and rise beautifully.
Step 2: Prepare the Baking Pan - Line a 9x9-inch baking pan with parchment paper, leaving some overhang on the sides for easy removal.
Step 3: Mix the Wet Ingredients - In a large mixing bowl, whisk together the melted butter, granulated sugar, brown sugar, eggs, and vanilla extract until smooth and creamy.
Step 4: Combine the Dry Ingredients - In another bowl, sift together the all-purpose flour and cocoa powder.
Step 5: Combine Wet and Dry Ingredients - Gradually add the dry mixture to the wet ingredients, stirring gently to combine.
Step 6: Fold in the Chocolate Chips - Once the batter is combined, fold in the chocolate chips and peanut butter chips.
Step 7: Prepare the Peanut Butter Swirl - In a small bowl, warm the peanut butter slightly in the microwave for about 15-20 seconds.
Step 8: Layer the Brownie Batter - Pour half of the brownie batter into the prepared pan, spreading it evenly. Then, drop spoonfuls of the warmed peanut butter over the brownie layer.
Step 9: Swirl the Peanut Butter - Use a knife or skewer to gently swirl the peanut butter into the brownie batter, creating a beautiful marbled effect.
Step 10: Bake the Brownies - Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Step 11: Cool and Slice - Once baked, remove the brownies from the oven and allow them to cool in the pan for about 10 minutes.
