Black-Bottom Banana Bars

1/2 cup butter or margarine
1 cup granulated sugar
1 egg
1 teaspoon vanilla extract
1 1/2 cups mashed ripe bananas (about 3 medium)
1 1/2 cups flour
1 teaspoon baking powder
1 teaspoon baking soda
1/2 teaspoon salt
1/4 cup baking cocoa

In a mixing bowl, cream butter and sugar. Add egg and vanilla extract; 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 x 9-inch baking pan. Spoon remaining batter on top and swirl with a knife. Bake at 350 degrees F for 25 minutes or until the bars test done.

Yields about 2 1/2 to 3 dozen bars. These bars are better the day after baking.