Cut the butter into small flakes and mix with the flour with the sugar, salt and egg yolk. Dissolve the yeast in lukewarm milk, add it as well and knead the dough until it shows bubbles. Then put in the heat for 45 minutes to walk before unrolling.
Peel and slice apples.
Roll out the dough and use it to line a 28 cm diameter springform pan. Spread the apple slices on the dough.
Bring 500 ml milk to the boil and stir in the semolina. Cook over a moderate heat for about 20-25 minutes until thick and pulpy. Then remove from the fire and stir in the sugar, vanilla sugar, sour cream and egg yolk. Finally, beat the egg white until stiff and fold in.
Now put the semolina on the apple slices. Sprinkle with cinnamon or sugar and cinnamon and the flakes of butter.
Bake in a preheated oven at 200 ° C for about 35-40 minutes.