Beat the eggs with the hot water with the hand mixer on the highest setting for one minute until frothy. Mix the sugar and vanilla sugar and sprinkle in gradually over a minute, then beat for another two minutes. Mix the flour, starch and baking powder. Sift half of it onto the egg cream and stir in briefly on the lowest setting. Stir in the rest of the mixture in the same way.
Spread the dough in a 40 x 25 cm baking pan with a raised rim (greased and covered with baking paper). Put the form in the oven and bake the sponge cake immediately. With hot air 180 ° C (preheated) 10-15 minutes. Turn the biscuit out onto a surface, e.g., Carefully peel off the baking sheet with parchment paper and the parchment paper. Let the dough cool down and if you have it, use a square baking frame to move it around. It`s just easier with a margin, if you don`t have one, you just have to be more careful with the cream on the dough later.
While the sponge cake is baking and cooling, detach the upper and lower halves of the milk bars from the milk bar cream, best to separate them carefully with a knife. Put the milk wafers cream in a bowl, put the milk wedge lids aside. Add the sour cream to the milk wedge cream and stir briefly on the lowest setting with the hand mixer. Whip the cream with vanilla sugar for 20-30 seconds, then add the two packets of cream stabilizer and whip the cream until stiff. Fold the cream into the milk wedge cream. Spread the entire cream evenly on the cooled sponge cake base.
Place the milk cake lids close together on the cream and press lightly. Chill the cake for at least two hours. If you had a baking rim around it, cut it all around and carefully remove it.