How to cook
Whip the eggs with the sugar into a thick foam, add the flour and vanillas or lemon zest. Bake in a moderate oven at 356°F (180 °C) until golden. Leave the cake layer to cool, then take it out of the form.
Carve out the cake layer, leaving a border of about 3/4″ (2 cm) thick and 1/4″ (0.5 cm) thick bottom. Optionally, you can syrup the cake layer with compote juice.
Caramelize the walnuts. Put about 1 cup walnuts in an oiled container (1 tbsp oil), pour on the caramel made from 5 tbsp sugar and 1/2 tbsp water. After the mixture cools, mash it finely.
Grind the dug out part of the cake layer into crumbs and mix it with the caramelized walnuts, sour cream, cocoa, powdered sugar and diced bananas. Stir everything well and pour it into the carved out cake. Make an optional decoration of chocolate and bananas.
The cake needs to sit in the fridge for at least 3 hours.