Warm the milk lukewarm. Crumble the yeast, stir with about 100 ml milk and 1 teaspoon sugar until smooth. Put the flour into a bowl and press a depression in the middle. Pour in the yeast milk and mix with some flour from the rim to the pre-dough.
Cover and leave to rise in a warm place for about 15 minutes.
Add the remaining milk, eggs, 80 g sugar, butter and 1 pinch of salt to the pre-dough. Knead everything into a smooth dough. Leave to rise for another 30 minutes.
Peel apples, remove core. Roughly grate apples. Mix with lemon juice and grappa. Knead into the dough. Cover and leave to rise in a warm place for 15-25 minutes.
Heat the oil in a deep fryer or pot (max. 180 °C). Use two damp tablespoons to cut dumplings from the dough, bake in portions in hot fat for 3-5 minutes until golden brown. Remove.
Drain the donuts well on kitchen paper.
Mix 150 g sugar with cinnamon. Turn the doughnuts in it. Serve with vanilla sauce.