Mix the flour and baking powder and sift into a bowl. Add sugar, vanilla sugar, butter and egg yolk and knead everything into a smooth dough. Divide the dough portion and roll out both halves between 2 layers of baking paper 38 x 20 cm. The thickness of the dough sheet results from this. Place both plates on a smooth, firm surface and place them in the refrigerator for approx. 30 - 40 minutes.

Preheat the oven to 180 ° O / bottom heat. Line the tray with baking paper or foil. Beat the egg white lightly with a whisk until it forms a small foam and keep ready with a little sugar. Take a sheet of dough out of the refrigerator, cut out circles with a 5 cm diameter cutter (with a wavy or smooth edge) and place them on the sheet with a gap. Then cut out a hole in the middle with a smaller cookie cutter approx. 1.5 cm in diameter and either bake these small plates or add them to the cookie cutter, knead, roll out again thinly, cool and cut out again until the dough is used up. Now brush the "donuts" (and possibly small flakes) with the slightly frothy egg white and do not sprinkle too sparingly with sugar. Then put the tray in the oven on the 2nd rail from the bottom. The baking time is 12-15 minutes.

Meanwhile, process the second sheet of dough. But just cut out the circles and distribute them on the sheet. They are not coated with sugar and have no hole in the middle. Here, too, knead the leftover dough again, roll out, cool and cut out. When cutting out both types, make sure that you make the same number. Bake the 2nd tray for 15 minutes as well.

Wash the lemon with hot water, dry it, completely rub off the peel and squeeze out the juice for 3.5 tbsp. While the biscuits are cooling, stir together a firm cream from all the ingredients using the hand mixer.

Always arrange the rings and whole biscuits in pairs for filling. Then spread a heaped teaspoon of cream on the closed cookie and put a curl on it.

The surface of the cookies is crisp due to the sugar crust and the cream gives them a lemony note.