Preheat the oven to 350 F and grease an 8x8 pan.

Melt the butter in a mixing bowl. Add the brown sugar, peanut butter, egg and vanilla and mix well. Mix in the flour, and fold in the chocolate chips and peanut butter chips. Pour the batter into the pan. Sprinkle the chopped up Reese's cups on top, along with some extra chips. Bake for 22-25 minutes, until the edges are golden brown. Wait about 30 minutes before cutting and serving.