Wash apples, grate dry, halve and remove core. Grate apples coarsely and mix immediately with lemon juice. Put fat, sugar, vanillin sugar and salt in a mixing bowl.
Cream with the whisk of the hand mixer until the sugar is dissolved. Gradually add eggs and stir. Mix flour, cornstarch and baking powder and stir into the dough by the spoonful.
Drain the grated apples on a sieve, add them to the dough with the hazelnuts and stir in carefully with a mixing spoon. Grease a box form (26 cm long) or line it with baking paper.
Pour in the dough and bake in the preheated oven (electric: 175 °C/ gas: level 2) for 60-75 minutes. After half of the baking time, cover with parchment paper if necessary. Remove the cake from the oven, let it cool down a little and carefully turn it out of the tin.
Let it cool down on a cake rack. Possibly decorate with candied apple slices and mint leaves. Makes about 14 pieces.