1/2 c unsalted butter
3/4 c granulated sugar
2 eggs
1 tsp pure vanilla extract
3 ripe bananas, mashed
2 c  flour
1 tsp baking soda
1/4 c sour cream

Preheat the oven to 350 degrees F. Butter a 9 inch springform pan (or heart-shaped pan.) Cream 1/2 cup butter until light. Gradually beat in the granulated sugar. Add the eggs one at a time and beat after each addition. Beat in 1 tsp. vanilla and the mashed bananas. Sift or mix together the dry ingredients and add to the batter alternately with the sour cream. Spoon the batter into the prepared pan evenly and bake for 30 to 40 minutes, or until the cake springs back when gently pressed in the centre. Cool for 10 minutes and invert. Cool on a wire rack.
 
 

4 oz  semisweet chocolate
2 tbsp cocoa
1/3 c milk
1/4 c unsalted butter
1 1/2 c icing sugar, sifted (more if needed)
1 tsp pure vanilla extract 
For the icing, melt the chocolate, cocoa, milk and 1/4 cup butter in the top of a double boiler. Cook until smooth and cool slightly. Beat in the icing sugar and 1 tsp. vanilla. Place the bowl over a larger bowl of ice and water and stir until the icing is spreadable. Ice the cake and decorate as you wish.