Marshmallow Squares

1/2 cup butter
3/4 cup brown sugar
2 eggs
1 tsp vanilla
3/4 cup flour
1/4 tsp baking powder
1/4 tsp salt
1/2 cup chopped walnuts
2 1/2 cups mini marshmallows
1 cup chocolate chips
1 cup peanut butter
1 1/2 Rice Krispies

Cream butter and sugar. Beat in eggs and vanilla. Add dry ingredients ; mix until smooth. Stir in walnuts. Spread batter in a greased 9x13 inch pan; bake for 15 minutes at 350 degrees F. Remove from oven and sprinkle over the marshmallows. Return to the oven for 3 minutes or less. Cool. Make the topping by melting the chips and peanut butter together over low heat. Remove from heat and cool slightly. Stir in the Rice Krispies and pour over the base. Chill.