Preheat oven to 350 degrees. Line a 9x13” pan with foil and spray with cooking spray.

Cream brown sugar and butter in the bowl of an electric mixer fitted with a paddle attachment. Add eggs and vanilla and beat until combined. Add baking powder, salt, and flour and mix.

Mix in 2-3 cups of mix-ins. You can use whatever you have on hand, or whatever you like. For this pantry-clean-out recipe, I used a mixed 1 cup of white and semi-sweet chocolate chips, 1/2 cup toffee bits, and 3/4 cup Reese’s Pieces. Stir all those into the batter.

Press into prepared pan (dough is sticky, spray your hands with cooking spray to avoid it sticking to your hands). Sprinkle 1/4 cup Reese’s Pieces over the top. You can use about 1/4 cup of anything you have for this step: M&Ms, chocolate chips, etc. It just makes them look prettier.

Bake at 350 for about 25 minutes. (Be careful not to overcook - the center will still be jiggly when you take these out of the oven and they will finish cooking and firming up as they cool.) Cool completely before slicing into squares.