Sift together the cocoa powder, baking powder and baking soda. Puree the sugar, bananas and eggs. Mix the sifted ingredients with the rest of the dry ingredients. Combine the coffee, milk and vanilla extract with the banana puree mixture.
Add the wet and dry mixtures together. Spray a non stick muffin pan with vegetable oil and bake at 300 degrees for about 15-20 minutes. Test for doneness by pushing on the top of a muffin--it should spring back. Cool for twenty minutes.