Preheat your oven to 350°F. Generously coat a 12-cup muffin tin with nonstick spray, then set it aside.

In a mixing bowl, cream together the softened butter, peanut butter, and light brown sugar until the mixture is smooth and fluffy. Add the egg and mix well. Gradually add in the flour, baking soda, and baking powder, stirring until just combined. Fold in the semi-sweet chocolate chips. Divide the cookie dough evenly among the muffin cups, pressing it down to form a base.

Place one chocolate peanut butter cup on top of each cookie dough base.

In a microwave-safe bowl, combine the unsalted butter and semi-sweet chocolate chips. Microwave on high for about 1 minute, stirring every 30 seconds until the mixture is smooth and fully melted. Remove from the microwave and whisk in the granulated sugar.

Beat in the eggs one at a time, making sure to mix thoroughly after each addition. Stir in the vanilla extract.

In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder. Gradually add the dry ingredients to the chocolate mixture, stirring until everything is well combined.

Spoon the brownie batter over each peanut butter cup, spreading it out evenly to cover the entire top.

Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Allow the brookies to cool in the pan for at least 45 minutes before removing them to enjoy.