For the sponge cake, separate the eggs. Whip the egg whites in a whisk until stiff and add the sugar. Egg yolks in the amount form and only with the whisk lightly stir in. Sift flour and cornstarch into the egg mixture and fold in gently.
Spread the bottom of a baking sheet with parchment paper. Spread sponge mixture evenly on the parchment paper. Smooth out and bake in the oven on the bottom rack for about 10 minutes until the sponge has turned a golden yellow color.
Meanwhile, for the filling, whip whipping cream, add cream cheese or low-fat curd, pureed berries or fruit juice, raw cane sugar and bourbon vanilla and stir until creamy.
Lay out a kitchen towel on a surface and sprinkle evenly with sugar. Remove the sponge cake base from the oven, turn the hot baking tray with the sponge cake base onto the kitchen towel with a lightning-fast twist of the hand, so that the sponge cake base is lying surface down in the center of the kitchen towel. Remove the baking tray and loosely roll up the kitchen towel together with the sponge cake base while it is still hot, so that the sponge cake base can later be formed into a roll. Repeatedly unroll everything on the spot and carefully peel off the parchment paper from the bottom of the sponge cake base, perhaps using a large knife.
Cut uneven edges of the sponge cake into small pieces and give to the helping child to eat form.
Cover the inside (nac