Step 1: Prepare for Baking
Preheat your oven to 350F (175C) and line a 9×9 inch baking pan with parchment paper. This ensures you can lift the brownies out easily later.

Step 2: Melt Chocolate and Butter
In a microwave-safe bowl, combine the butter pieces and chopped chocolate. Heat in the microwave for 30 seconds, stir well, and continue heating in 20-second increments until completely melted and smooth.

Step 3: Add Cocoa
Immediately whisk the cocoa powder into the warm chocolate mixture until fully combined and set it aside.

Step 4: Beat Eggs and Sugar
In a separate large mixing bowl, use an electric mixer to vigorously beat together the sugar, eggs, and vanilla extract. Continue for about 1 minute on medium-high speed until the mixture is lightened in color and pale yellow.

Step 5: Combine Mixtures
Drizzle the chocolate mixture into the egg mixture and stir until the batter is uniform and completely combined.

Step 6: Incorporate Dry Ingredients
Sift the flour and salt over the mixture. Stir until the flour is completely absorbed. If you are using mini chocolate chips, fold them in now.

Step 7: Assemble the Layers
Measure out about 2 tablespoons of peanut butter and set it aside for the topping. Spread exactly half of the brownie batter evenly into the bottom of the prepared pan.

Step 8: Add Peanut Butter
Dollop the remaining larger portion of peanut butter over the batter. Use the back of a spoon to gently smooth it, leaving about 1/4 to 1/2 inch of space around the perimeter.

Step 9: Top and Swirl
Gently dollop the remaining brownie batter over the peanut butter and nudge it to the edges so the peanut butter is covered. Finally, dollop the reserved 2 tablespoons of peanut butter on top and use a knife to gently swirl it into the batter.

Step 10: Bake
Transfer to the center rack and bake for 35–40 minutes. The brownies are done when a toothpick inserted into the center comes out clean or with a few moist crumbs.

Step 11: Cool
Allow the brownies to cool completely in the pan before serving.