For the short pastry, separate 1 egg. Work through the fat, 125 g sugar, flour and 1 egg yolk with the dough hooks of the hand mixer. Then knead with your hands to a smooth dough. Cover and chill for about 30 minutes.
In the meantime drain the apricots thoroughly. Roll out the dough on a floured baking tray. Prick several times with a fork. Bake in the preheated oven (electric: 200 °C/ gas: level 3) for about 18 minutes.
Separate 3 eggs for the glaze. Mix sour cream, milk, 50 g sugar, 3 egg yolks, 1 whole egg and lemon juice. Spread the apricots on the dough. Pour the icing over the apricots. Bake in the preheated oven (electric: 175 °C/ gas: level 2) for about 40 minutes.
In the meantime, beat 4 egg whites until stiff, add 175 g sugar. Fold in the hazelnuts. Spread the beaten egg whites on the cake and bake at high heat or under the preheated grill until golden brown.
Results in about 20 pieces.