Black Bottom Banana Bars

Apparently, I'm not buying bananas according to Eric's preference.  Apparently, he wants them bought when they are literally green and not even remotely ripe.  I buy bananas that are yellow so when he lets me go to the grocery store alone, I buy enough yellow bananas for the both of us for the week and byTuesday, he apparently has had his last banana.  Whatever.  He gives me an excuse to bake then.

1/2 c butter, softened
1 c sugar
1 egg
1 tsp vanilla extract
3 medium ripe bananas, mashed
1 1/2 c all purpose flour
1 tsp baking powder
1 tsp baking soda
1/4 c baking cocoa powder

Preheat oven to 350 F.  Grease a 13x9 pan.  In a large bowl, beat butter and sugar until fluffy.  Add egg, extract, and bananas.  Beat until well combined.  Combine flour, baking powder and baking soda.  Add to butter mixture and beat until just combined.  Divide batter in half.  Add cocoa powder to one half of batter and beat well.  Spread cocoa mixture into pan.  Spoon other half of batter on top of cocoa mixture.  Bake 25 minutes or until fork comes out clean.