Cream butter and sugar. Add vanilla and eggs.
Combine and add flour, baking powder, and cocoa. Stir in nuts. Spread into greased 9x13 inch baking pan. Bake in a 350° oven for 15 minutes. Remove from oven and sprinkle 2 cups marshmallows evenly over baked top. Return to oven to melt a bit. Remove from oven and spread with frosting.
Frosting: Melt 6 ounces chocolate chips and 1 cup peanut butter over low heat. Add ½ cups Rice Krispies. Spread over top. Cool and cut into bars. Bars freeze well.
