Prepare the Baking Pan: Begin by preheating the oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper or lightly grease it with butter. This step helps the brownies release easily after baking and makes cleanup much easier.
Mix the Butter and Sugars: Pour the melted butter into a large mixing bowl and add the granulated sugar and brown sugar. Whisk everything together until smooth and glossy. This mixture forms the base of the brownies and helps create their rich texture.
Add the Eggs and Vanilla: Crack the eggs into the bowl one at a time while mixing. Stir well after each addition so the batter becomes thick and smooth. Add the vanilla extract next and continue mixing until everything blends together evenly.
Combine the Dry Ingredients: In another bowl, whisk together cocoa powder, flour, salt, and baking powder. Slowly add this dry mixture into the wet batter while stirring gently. Continue mixing just until the ingredients combine and the batter becomes thick and chocolatey.
Layer the Batter and Peanut Butter Cups: Spread about half of the brownie batter into the prepared baking pan. Place the mini peanut butter cups evenly across the surface, leaving small gaps between them. Spoon the remaining batter on top and carefully spread it so the candies are fully covered.
Add Optional Toppings: Sprinkle chocolate chips or chopped peanut butter cups over the surface if you enjoy extra chocolate flavor. These toppings melt slightly during baking and add more texture to the finished brownies.
Bake the Brownies: Slide the pan into the oven and bake for about 30 to 35 minutes. The edges should look set while the center remains slightly soft. Insert a toothpick near the edge to check for doneness since the peanut butter cups in the middle will stay creamy.
Cool and Slice: Allow the brownies to cool completely in the pan before cutting. As they rest, the chocolate firms up and the peanut butter layer settles. Once cooled, slice the brownies into squares and serve.
