Warm up the milk. Melt butter in it. Mix 400 g flour, yeast, sugar and 1 pinch of salt. Add egg and egg yolk. Add warm milk-butter mixture. Knead the dough first with the dough hooks of the mixer, then with your hands for 5-6 minutes to a smooth dough.
Form the dough into a ball and put it back into the bowl. Cover and leave to rise for approx. 1 1⁄2 hours in a warm place. Knead the dough again with your hands. Then let it rest in the fridge for at least 3 hours.
Knead dough briefly, roll out and 13-15 donut rings (à approx. 8 cm Ø; various sizes at e.g. amazon.de from 6 € plus shipping, alternatively cut out the outer circle e.g. with a glass. For the lo
So that nothing sticks, dip both briefly in flour). Cover the dough rings and let them rise. Fry in portions. Lift them out and let them drip off briefly on kitchen paper. Turn donuts in sugar while still hot, let them cool down.
For the casting, whip the sour cream with the whisks of the mixer for 1-2 minutes. Fold in marshmallow cream until the icing is thick and creamy. Stir nut nougat cream until smooth and fold into the marshmallow cream in streaks.
Spread on the donuts and serve immediately.