This cake combines all the best dessert flavours with tender chocolate layers. The filling is so smooth and rich, it almost resembles ice-cream. Bananas and coffee pair very well, and a bit of rum only enhances the flavours. The sour cream you use in the cake layers makes them more tender and moist as well as easier to slice in half or even carve.
Don't be intimidated by the amount of milk you use to brush the layers, it will not make the cake soggy, it will just keep it very moist for days. As always, make sure you use the highest quality chocolate, as it does contribute quite a bit to the flavour. Also, it keeps the filling firmer. Serve the cake very well chilled, and I do recommend you put it in the freezer for about 30 minutes before serving, it makes it even better.
For the cake layers
200 grams all purpose flour
50 grams cornflour (corn starch)
2 teaspoons baking powder
150 grams sugar
50 grams unsweetened cocoa powder
120 ml oil
30 ml dark rum
200 grams sour cream
For the topping
120 ml chocolate milk
2 teaspoons vanilla
For the filling
150 grams ripe bananas
50 grams instant chocolate pudding
2 tablespoons instant espresso powder
150 ml whole milk
100 grams dark chocolate
200 ml heavy whipping cream
1 ½ teaspoon unflavoured gelatine powder
For the cake, sift the flour with the cornflour (corn starch), cocoa powder and baking powder twice, and set it aside. Beat the eggs and sugar with an electric mixer on high for about 3-4 minutes, until the batter becomes pale and thick. Pour in the oil and rum and blend it well, then gently mix in the sour cream. In the end, tip in the dry ingredients and whisk until just incorporated, do not overmix the batter. Generously butter the base and sides of a spring-form pan (23cm, 9"), pour in the batter and bake in a preheated oven, at 170˚C (340˚F) for about 25 minutes, and make sure you do the toothpick test. It is very important that the cake stays moist. Leave it in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.
For the filling, melt together the chocolate and half of the heavy cream (using a double boiler or the microwave), and let it cool down slightly. Mash the ripe bananas very well, with a fork or in a food processor. Transfer it to a large bowl, add in the espresso powder, milk and the instant chocolate pudding and beat with an electric mixer on high for about 2 minutes, to blend everything well. When the Ganache is just barely warm, mix it with the banana-pudding mixture. Use a spatula or a wooden spoon. Pour 5 teaspoons of cold water over the gelatine and leave it for at least 10 minutes to activate. Whip the heavy cream until stiff peaks form. Dissolve the bloomed gelatine over low heat (or in the microwave), but be careful not to let it boil; take a little bit of the whipped cream, stir it in the dissolved gelatine and then pour it in the whipped cream and beat a little more, to incorporate. Finally, gently fold the whipped cream in the chocolate batter, using a spatula.
To assemble, level the top of the cake if you need, and gently slice it into three layers. Turn both layers so the cut side is up, then brush off any crumbs and place the first layer and put it on your serving platter. Place the spring-form pan ring around it, close it, brush it with a third of the milk, and gently spread the half of the filling evenly. Take another cake layer and put it on top, gently flatten it with your palm, then brush it with the milk mixture. Spread the other half of the filling, and top with the third layer. Brush the last layer with the rest of the milk, cover the surface with cling film and put it in the refrigerator for at least 8 hours, or overnight. Decorate to your liking and serve well chilled.