1. Preheat the oven to 350°F (180°C). Line a 9.5 inches (24cm) springform tin with baking parchment and grease lightly. Set aside.

2. Add butter and sugar to a large bowl and mix on high speed until light and fluffy. Add the eggs one after another and mix well after each addition. Add vanilla extract and mix in. Mix the flour with cocoa powder, baking powder, and salt, then add together with the milk to the bowl and mix on low speed until just combined. Add the chopped chocolate and fold in. Pour the batter into the prepared springform tin, smooth out the top and bake for 25-28 minutes or until a wooden skewer inserted into the center comes out clean. Take out of the oven and let cool down completely on a wire rack.

3. Add the cold heavy cream and vanilla extract to a bowl and mix until frothy. Add the cream stiffener and whisk until stiff peaks form. Add the chopped chocolate and fold in.

4. To assemble the cake you have to scoop out some of the insides of the cake layer – you should leave a base with a thickness of about 0.4 inches (1cm) and a border of about 0.4-0.8 inches (1-2cm) – you should get something like a very shallow bowl. Gather the cake scraps. Peel the bananas and cut them into 0.4 inches (1cm) thick slices. Place the banana slices in the hollowed-out cake layer to get an even layer that covers the base. Add a small portion of the whipped cream on top of the banana slices and press into the gaps between them. Pile up the remaining cream to create a dome that is flush with the edges. Crumble the cake scraps to get fine crumbs and press them gently all over the cream to cover the dome completely. Place in the fridge for about 30 minutes before serving.