1: In a cup mix 20 g yeast with 4 tablespoonsful of warm milk. Leave to ferment for 30 minutes at room temperature. This makes a yeast-based "leaven" which improves the flavour of the doughnuts.
2: After this time, put 40 g caster sugar, 50 g butter and 350 g flour into a food-mixer bowl with the rest of the milk.
3: Pour in the yeast leaven liquid and knead on slow speed until the dough is evenly mixed.
4: Gather the dough into a ball and put this into a clean bowl. Cover with a plastic sheet and leave to rest for 2 hours at room temperature.
5: After this time, roll out the dough and shape the doughnuts as shown in this video. Once they are all on the baking sheet, cover with a plastic sheet again and leave to rest for 1 hour.
6: Heat the oil to 180°C (360°F) and lower in the doughnuts. Fry until golden brown...
7: ...on both sides.
8: Sprinkle the cooked doughnuts with caster sugar.