For the milk bread, first prepare the sourdough. For this, stir flour and starter with 35 ml of warm water to a dough and let it rest for about 16 hours in a warm place.
For the pre-dough, mix flour, yeast and 20 ml water to a dough and let it rest in the refrigerator for about 16 hours.
For the main dough, knead sourdough, pre-dough and the remaining ingredients in a food processor to a strong dough. And let rest for 15 minutes.
Then knead the dough well again on a lightly floured work surface and shape into a loaf. Place in a well-greased baking pan (box) and let rest again, covered, for about 1 hour.
Preheat the oven to 250 °C, whisk the egg and brush the bread with it. After baking for about 5 minutes, turn the oven temperature down to 210 °C and bake for about 35 minutes.
Steam the oven well during this process.