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 butterscotch chips,1/2 cup peanut butter chips, and Nutter Butters. 

Press into prepared pan (dough is sticky, spray your hands with cooking spray to avoid it sticking to your hands). Bake at 350 for 23 minutes. Remove from oven and sprinkle remaining peanut butter chips over the top of the hot bars. Return to oven for 2 minutes. Remove from oven and carefully spread the melting chips over the top of the bars to create a frosting. Sprinkle with sprinkles and let cool. (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.