Black Bottom Banana Bars

½ cup margarine, softened
1 cup sugar
1 egg
1 tsp. Vanilla
1-½ cups mashed ripe bananas (about 3)
1-½ cups flour
1 tsp. Baking powder
1 tsp. Baking soda
½ tsp. Salt
¼ cup baking cocoa

In a mixing bowl, cream margarine 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 13x9x2 baking 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.