1/2 c. softened butter
1/4 c. peanut butter
1 c. sugar
1 c. packed brown sugar
3 eggs
1 tsp. vanilla
2 c. flour
2 tsp. baking powder
1/2 c. (or 5.5 oz. can) Hershey's chocolate syrup

Preheat oven to 350 degrees. Blend butter and peanut butter in large bowl. Add sugars; beat well. Add eggs, one at a time, blending after each egg. Blend in vanilla. Combine remaining dry ingredients and mix well. Spread 1/2 batter in greased 13 x 9 pan. Spoon syrup over top. Carefully spread remaining batter over syrup and swirl with knife for marbled effect. Bake 35 to 40 minutes, then cool and cut into squares.