Stir all ingredients until a smooth dough is obtained.
If you have a mixer, you can knead the dough with it. To do this, stir for 5 minutes using a mixer with dough attachments, first at the lowest and then at the highest speed.
Cover the dough and place it in a warm place until it suits.
Sprinkle flour on the table. Remove the dough from the bowl and knead a little again on a lightly floured work surface. Then roll out the dough in a layer of 1 cm.
Squeeze out dough circles in a round shape (diameter ≈ 7 cm). Cover the mugs again and place them in a warm place until the dough is even better (≈ 15 minutes).
Bring the oil to a boil in a cauldron, deep fat fryer, or heavy-bottomed saucepan. Layout the prepared dough circles.
Fry mugs of dough in portions in boiling deep fat on both sides for 3-5 minutes until light brown.
Remove them with a slotted spoon and put them on a wire rack covered with a double-folded paper towel so that the fat drips onto it.
For the filling, fill a culinary syringe with a long narrow tip with jam or plum puree and add portions to donuts.
Pour the remaining sugar into a plate. Dip the Berlin donuts in sugar.