Black-Bottom Banana Bars

Black-Bottom Banana Bars
This recipe came from Taste of Home, Collector's Edition.

1/2 c. butter
1 c. sugar
1 egg
1 t. vanilla extract
1 1/2 c. mashed bananas, about 3 medium
1 1/2 c. flour
1 t. baking powder
1 t. baking soda
1/2 t. salt
1/4 c. cocoa
Cream butter and sugar. Add egg and vanilla; beat until thoroughly combined. Blend in the bananas.
Combine the flour, baking powder, baking soda and salt; add to creamed mixture and mix well.
Divide batter in half. Add cocoa to half; spread into a greased 13"x9"x2" pan. Spoon remaining batter on top and swirl with a knife. Bake at 350 degrees for 25 minutes or until the bars test done. Cool and cut into bars.