Mix flour with yeast and salt. Form a hollow in the middle.
Heat the cream or milk (should not be too hot!). Mix two eggs and one egg white, as well as sugar, vanilla sugar, lemon zest and cream/milk with a hand mixer or a whisk.
Pour into the well and knead well by hand until a smooth dough is formed.
Moisten the dough with a little water and cover with a kitchen towel. Leave in a warm place until doubled in volume.
Preheat oven to 160 °C hot air or 180 °C top/bottom heat. Then knead the dough briefly on a floured work surface and divide into three equal parts.
Form an approx. 30-40 cm long roll from each of the parts. Line a baking tray with baking paper and braid the rolls into a plait.
Whisk the egg yolk with 1-2 tablespoons of milk and brush the braid with it. Sprinkle with hail sugar.
If you are not satisfied with the volume of the dough, leave the plait in a warm place for another 20 minutes until it has reached the desired volume (be careful! The plait will rise even more during baking).
Bake the yeast plait for about 30 minutes until it has taken on a golden yellow color.
Serve warm (e.g. with milk or cocoa) or let cool and pack airtight.