First stir the eggs, salt, sugar and oil until frothy. Then add the flour, baking powder and milk. Put the dough in a greased and floured 26 cm springform pan. Dice the apples and spread them on the dough.
Bake the cake in a preheated oven at 180 degrees for 30 minutes.
For the topping, mix together the butter, sugar, vanilla sugar and egg.
Remove the cake, spread the mixture on top and then bake in the oven for another 10 minutes.
Let the cake cool down after the baking time and sprinkle with powdered sugar.