How to cook
Combine the warm milk, sugar and melted butter in a mixing bowl and beat with a whisk to melt the sugar. Mix the flour with the yeast, add it gradually to the other mixture, beating with whisk at first, then kneading with your hands.
Leave the resulting solid dough to rise for about 45 minutes, to increase in volume. Roll out a dough to a thickness of about 1/2″ (1.5 cm) and use a glass to cut out circles.
Arrange the circles on clean towels and cover to rise again for about 20 minutes until slightly bulged. Heat oil for frying, but don't have the stove on too high. Use enough oil to have a depth of 1/4″ (0.5 cm). Fry the Berliners on both sides until brown. If fried right, they will have a characteristic bright ring in the middle.
Leave them to cool. In the meantime, blend the jam and put it in a pastry bag. Drill each Berliner in its the side and fill it with jam. Finally, sprinkle with powdered or granulated sugar and crushed walnuts. You can decorate the cooled Berliners with frosting.
If you do not want to fill Berliners, coat them with sugar while still hot and eat them immediately.