For the bottom, preheat the oven (electric cooker) to 175 °C. Beat the eggs, sugar and vanilla sugar until light and very frothy. Melt the butter, whisk with the milk and stir into the egg mixture.
Mix flour, baking powder and salt and carefully fold into the dough.
Pour the dough into a greased springform pan sprinkled with breadcrumbs. Bake in the middle of the preheated oven for about 30 minutes. Check with a skewer if the dough is baked through.
Nothing must stick to it. Allow the cake to cool slightly, then drop it onto a cake rack.
For the meringue, separate the eggs (no yolk must get into the egg white!). Put the egg whites, sugar and lemon juice in a mixing bowl. Whisk vigorously over a hot water bath with the whisks of the mixer until the mixture has reached a temperature of 65 °C.
The beaten egg white should be firm and the sugar completely dissolved. Remove from the water and continue beating until the mixture has cooled down. Add the flaked almonds.
Heat the oven grill to 250 °C. For the filling, bring water and sugar to the boil, remove from heat and flavour with rum. Add the berries and leave to cool.
Cut the sponge cake base into 3 cm thick slices and line a casserole dish with a high rim. Drizzle the marinated berries and a little of the marinade over the sponge cake. Cut the very hard frozen ice cream into 3 cm thick slices or use an ice cream scoop to cut them off and place them on the berries.
Cover the ice cream completely with beaten egg white and bake for 4 minutes with the oven door open until the meringue is golden yellow. Serve immediately.