These are yummy kids, but I don't know why they're called "black bottom" mine were'nt...here's what you do>>>
1/2 Cup butter, softened
1 cup sugar
1 tsp vanilla
1 1/2 cups mashed ripe bananas (about 3 medium)
1 1/2 cups flour
1 tsp. baking powder
1 tsp. baking soda
1/2 tsp. salt
1/4 cup cocoa
Cream butter and sugar in mixing bowl. Add egg and vanilla, beat thoroughly. Blend in bananas-combine flour, bak. powder, bak. soda and salt in separate bowl-add to creamed mixture and mix well. Divide batter in half, only add cocoa to one of those halves(got it?) Spread the half with the cocoa in greased 9x13 pan, spoon the rest of batter on top and swirl with a knife.
350 degree oven for about 30 minutes, test before that cuz you don't want them too done, they dry out and they are better kinda fudgy like (you know what I'm sayin') Enjoy!!