Boil the water with butter, salt and vanilla sugar, then add the flour and stir until the mixture loosens from the pan.
Cool the mixture a little and then stir in the eggs one by one until the mixture is smooth and shiny. Let the dough rest.
In the meantime, make a biscuit from the biscuit ingredients, spread it on a baking sheet lined with baking paper and bake for approx. 10-15 minutes at 200 ° C and refrigerate.
Brush the baking sheet with butter or margarine, dust with flour and spread the choux pastry on top. Bake at 220 ° C in a preheated oven for approx. 20-25 minutes, do not open the oven for the first 15 minutes. If the pastry has lost some color, turn the heat down to approx. 160 ° C and finish baking.
Bring milk to the boil and cook a pudding from milk, pudding powder and sugar.
Stir the softened gelatine into the still hot pudding and chill, but do not let it set.
When the pudding is cold, carefully add the whipped cream with vanilla sugar.
Smooth out the cooled sponge dough and place the cooled choux pastry base on top.
Just before serving, dust with icing sugar.
Tip:
Mountain cake with vanilla cream and sour cherries:
Drain 2 glasses of sour cherries from juice and about 3 tablespoon. Boil the cornstarch pudding, mix in the cherries, spread on the sponge cake and cool.
Make only 2/3 of the vanilla cream, smooth it out on the sour cherries and place the choux pastry base on top.