Warm the milk in a small pot lukewarm. Crumble yeast into the milk and dissolve it completely while stirring. Put 500 g flour, 100 g sugar, 1 pinch of salt, ##eggs## and butter in flakes in a large mixing bowl.
Pour yeast milk into the mixing bowl and knead everything with the dough hooks of the mixer to a smooth and supple dough. Cover and leave to rise in a warm place for about 45 minutes.
Knead the dough again with floured hands. Roll out to a thickness of about 2 cm on a little flour. Cut out approx. 14 circles (each approx. 7 cm Ø). Put them on baking paper and let them rise for about 30 minutes.
##Fry fat## in a wide pot to approx. 180 °C (it is hot enough when bubbles rise from a wooden skewer). Add Berliner in portions so that they can swim without sticking together.
Bake for 7-8 minutes until golden brown, turning once.
Lift out the doughnuts with a skimmer and let them drip off on kitchen paper. Turn one half of the doughnut while still hot in about 100 g sugar. Fill jam into a piping bag with filling spout. Pour some jam into the side of each doughnut.
Let it cool down.
Mix icing sugar and 2-3 tablespoons of water to a spreadable glaze. Coat the surface of the unsweetened doughnuts with it. Allow to dry. Eat the doughnuts very fresh.