Preheat oven to 350 F and grease and flour a 10 inch round cake tin.
Beat egg whites with half of the sugar until stiff peaks form in a mixing bowl.
In a separate bowl, beat the butter with remaining sugar until foamy. Slowly stir in the egg yolks. Mix in flour, cocoa powder, baking powder, and ground almonds until a smooth batter forms. Fold in beaten egg whites. Transfer the batter to the prepared pan and bake in the preheated oven for 25-30 min. Allow to cool completely on a rack.
Meanwhile, put 4 tbsp cold water into a small heatproof bowl and sprinkle the gelatin over. Soak for 5 minutes, then put the bowl in the microwave and heat for 10 seconds. Whip the cream until almost stiff, then add the gelatin. Continue whipping the cream until it forms stiff peaks.
Using a knife, cut around the edge of the cake base to form a ring approximately 1 inch from the outside of the cake. Do not cut all the way through to the bottom! Use a spoon to hollow out the center of the cake. Crumble the spooned out cake into a bowl with your hands.
Puree 1 banana in a separate bowl using an electric beater or fork. Add the vanilla extract and powdered sugar to the whipped cream with the pureed banana and chocolate chips. Chill for 30 minutes.
Cut the remaining bananas lengthwise to make two halves from each. Lay these face down alongside each other inside the cake cavity. Scoop the cream filling on top, arranging it into a molehill shape, so that the middle is higher than the edge. Top the cream with the crumbs you have made, coating it completely. Leave to chill in the fridge for 1-2 hours and serve cold.