Separate eggs. Beat the egg whites and mineral water with the whisk of the hand mixer until stiff and finally add 125 g sugar. Beat the egg yolks one after the other. Mix flour, starch and baking powder, sieve onto the egg mixture and fold in carefully. Put the dough on a baking tray (32 x 39 cm) lined with baking paper and smooth it down. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 14 minutes. Remove the sponge cake from the oven, turn out on a damp tea towel and let it cool down
Clean, wash and halve the strawberries. Mix 2 tbsp. sauce powder and 60 g sugar. Whip the cream with the whisk of the hand mixer until stiff, pouring in the sauce powder-sugar mixture
Cut the sponge in half crosswise. Cover one half with a baking frame and sprinkle with the remaining sauce powder. Place strawberries on top, except for about 100 g for decoration. Spread vanilla cream on the strawberries and smooth it down. Place the second half of the sponge cake on top and press down a little. Remove the baking frame. Dust the cake with icing sugar and cocoa, cut into 18 pieces and serve on a plate
Waiting time approx. 20 minutes