Preheat oven to 350 degrees Fahrenheit and line an 8x8" pan with foil so the foil hangs over the sides about an inch. No need to grease foil.

In the bowl of an electric mixer, cream together peanut butter, brown sugar, eggs, vanilla and butter. Add in baking powder and flour and mix until combined.

Separate dough into two equal portions. Grab one portion and press on the bottom of the pan. Bake for ten minutes, then remove from oven and allow to cool completely. Sprinkle peanut butter cup candies over the baked dough, then spread marshmallow creme over the top of the candies. I found it easiest to quickly heat the marshmallow creme in the microwave (just a few seconds), then plop it in the middle of the pan and carefully spread outward from there.

Take the dough that you set aside and grab small portions, flatten them out in your hands, then place them on top of the marshmallow creme, piecing them together, until all the dough is gone. Place the pan back in the oven and bake for an additional 20 minutes, or until sides start to turn a slight golden brown. Let cool, slice and serve.