1/3 c. butter
1/2 c. peanut butter
1 1/2 c. brown sugar
2 eggs
1 1/2 c. flour
1 1/2 tsp. baking powder
1/2 tsp. salt
1/4 c. milk
1 tsp. vanilla

FROSTING:

1/4 c. butter
2/3 c. peanut butter
4 c. powdered sugar
1/2 c. milk
1/2 c. semi-sweet chocolate chips

Grease 10 x 15 pan; mix base and pat into pan, bake 18-20 minutes at 350 degrees. Cool, then frost with frosting. Melt chocolate chips and drizzle over frosting.