1/2 cup butter, softened
1 cup sugar
1 egg
1 tsp. vanilla
1 1/2 cup mashed ripe bananas (about 3 medium)
1 1/2 cup all purpose flour
1 tsp. baking powder
1 tsp. baking soda
1/2 tsp. salt
1/4 cup cocoa powder

In a mixing bowl cream butter and sugar. Add egg and vanilla, beat until thoroughly combined. Blend in the bananas. Combine flour, baking powder, baking soda and salt. Add to creamed mixture. Divide batter in half. Add cocoa to half. Spread into a greased 9 x 13 in. pan. Spoon remaining batter on top and swirl with a knife.

Bake at 350°F for 25 minutes or until toothpick inserted near center comes out clean. Cool. Cut into bars.