Preheat the oven to 350°F. Grease an 8×8 or 9×9 pan. For easy removal of the brownies, place parchment paper on the bottom and 2 sides of the pan. Grease again and then set aside.
Melt butter. While the butter is still hot, transfer into a large bowl. Add chocolate chips and white sugar and whisk until well combined. It will be thick and grainy, trust the process!
1 cup butter, 2 cups white sugar, 1/2 cup dark chocolate chips
Whisk in one egg at a time. Then whisk in the vanilla. The mixture should look glossy and smooth.
4 eggs, 1 tbsp vanilla
Fold in both cocoa powders, flour, baking powder, and salt. Make sure you don't over mix. The brownie batter will be thick.
1 cup all-purpose flour, 1/4 cup dark cocoa powder, 1/2 cup unsweetened cocoa powder, 1/2 tsp salt, 1/2 tsp baking powder
Spread evenly in the prepared pan. Dollop peanut butter across the entire pan and use a butter knife to swirl it in.
1/2 cup creamy peanut butter
Bake for 40-50 minutes. Mine took 50 minutes. The edges will be set, and the middle will jiggle. It will keep baking once pulled out of oven. Let cool completely before slicing. Top off with mini chocolate chips and cut up Reese's if desired.
12 Reese's peanut butter cups, 1/4 cups mini chocolate chips