Pour the milk into a bowl, add the crumbled yeast and mix with the milk. Add a quarter of the flour and 1 teaspoon of sugar and stir into a very soft pre-dough. Cover and leave to rise in a warm place for 30 minutes.
Add the rest of the flour, sugar, eggs, oil and salt to the pre-dough and chain everything well. Cover the dough and let it rise for another 20 minutes, then knead it again.
Place the dough on a floured work surface, form a roll and cut into 16 equal slices. Press the slices of dough evenly flat and cut a hole in the middle (with a cookie cutter approx. 3 cm in diameter) to form rings.
Place the rings on a floured surface and let them rise for another 20 minutes.
Heat the oil in a pot or deep fryer to 180°C. Place donuts in portions in the hot oil and fry until golden brown on both sides.
Drain donuts on the kitchen paper and when they are cold, dust with icing sugar or cover with chocolate icing.