1Preheat oven to 350 degrees F (180 degrees C) and place rack in the center of the oven. Butter, or spray with a non stick vegetable spray, a 9 x 13 inch (23 x 33 cm) pan. Set aside.
2In a large bowl whisk together the sugar, flour, cocoa powder (sifted), baking powder, baking soda, and salt. Set aside.
3In another large bowl, whisk together the eggs, mashed bananas, water, milk, oil, and vanilla extract.
4Add the wet ingredients to the dry ingredients and stir, or whisk, until combined. You will notice that the batter is quite thin. Pour the batter into the prepared pan and bake for about 35 to 40 minutes or until a toothpick inserted in the center of the cake comes out clean.
5Remove from oven and let it cool on a wire rack for about 30mins to 1 hr. when completely cooled, frost with the ganache
Place the chopped chocolate in a medium sized stainless steel, or heatproof bowl. Set aside. Heat the cream and butter in a medium sized saucepan over medium heat (can also be heated in the microwave). Bring just to a boil. Immediately pour the boiling cream over the chocolate and allow to stand for 5 minutes. Stir until smooth. When Ganache has completely cooled, beat until soft and fluffy (I use a wire whisk). Then spread the frosting on top of the cake.