Sponge: Beat the egg whites until very stiff and gradually add the sugar. Mix flour and cornstarch and sift into the egg mixture. Fill the dough into a springform pan and bake at 200 °C for about 45 minutes. After cooling, cut through 2 times.
Quantity: Soak gelatine in cold water. Remove peel from mango, cut off and mash with mango juice. Cut strawberries into small cubes and add to mango puree. Whip the cream until stiff. Squeeze out the soaked gelatine, warm it up and add to the mango and strawberry mixture. Immediately fold into the whipped cream.
Cake assembly: Spread sheet with plastic wrap and place springform rim on top. Cut decorative strawberries into narrow slices and spread evenly in the ring. Form a layer (1/4) of the whipped cream fruit mixture on top of the strawberries. Place first sponge cake layer on top, then spread next layer of whipped cream (1/4) on top of sponge cake. Place second sponge cake layer and fill with another quarter amount. Cover with the last sponge cake layer and refrigerate for one night.
Decorating: turn the precooled cake onto a cake plate, remove the cling film and take off the ring. Use the last quarter amount to brush the edge of the cake, or pipe rosettes around the edge.