I added chocolate chips to the banana layer - yum!
Black-Bottom Banana Bars Recipe
1/2 cup butter, softened
1 cup sugar
1 teaspoon vanilla extract
1-1/2 cups mashed ripe bananas (about 3 medium)
1-1/2 cups all-purpose flour
1 teaspoon baking powder
1 teaspoon baking soda
1/2 teaspoon salt
1/4 cup baking cocoa
1. In a large bowl, cream butter and sugar until light and fluffy. Beat in egg and vanilla. Stir in the bananas. Combine the flour, baking powder, baking soda and salt; add to creamed mixture and mix well.
2. Divide batter in half. Add cocoa to half; spread into a greased 13-in. x 9-in. baking pan. Spoon remaining batter on top and swirl with a knife.
3. Bake at 350° for 25 minutes or until the a toothpick inserted near the center comes out clean. Cool on a wire rack.