Sift All-Purpose Flour (125 gram), Unsweetened Cocoa Powder (40 gram), Baking Soda (3/4 teaspoon), Baking Powder (3/4 teaspoon) into a bowl and combine well with Salt (1/8 teaspoon) and Caster Sugar (130 gram).
Combine Banana (250 gram), Corn Oil (60 milliliter), Water (60 milliliter), Milk (120 milliliter),Vanilla Extract (1 teaspoon) in another bowl with Egg (1). Stir well with a hand whisk then pour them into the dry ingredients.
Preheat oven to 350 degrees F (180 degrees C).
Pour batter mixture into half-sphere - greased with Butter (to taste). Bake in preheated oven for about 25 minutes or till skewer inserted into center of the cake comes out clean.
Let cakes cool completely in the mold. Remove from mold and refrigerate for about 10 minutes for easier ganache frosting in the next step.
Prepare ganache cream: place Semi-Sweet Chocolate Chips (120 gram), Bittersweet Chocolate (120 gram) and Butter (35 gram) into a bowl. Bring Whipping Cream (185 milliliter) to boil at medium heat. Turn off heat and pour over the chocolates.
Pour ganache over cakes and refrigerate for 5 minutes. Pour over a second ganache layer to get a smooth frosting.
Refrigerate for another 5 minutes to set. Dust cakes with some Powdered Confectioners Sugar (to taste) or decorate as desired.