Dissolve the yeast in the lukewarm milk, add sugar and 2 tablespoons flour, stir and let rest for about 10 minutes. In a mixing bowl, knead the remaining flour with salt, oil, sour cream and the activated yeast into a smooth dough, brush the dough with a little oil and then let it rest for approx. 45 minutes until it has increased in volume. Divide the dough into 20 pieces, roll out all the balls very thinly and roll them up lengthways. Place on a baking sheet and brush with the oil-milk mixture. Let rest for another 10 minutes. Bake in the preheated oven at 200 ° C top / bottom heat for 10 minutes. The baking time can vary, it depends on how thinly the croissants were rolled. For the topping, mix the flour with the salt and gradually add a little water at a time, the consistency should be like that of a pancake batter. After 10 minutes of baking, take the croissants out of the oven and sprinkle with the topping, then bake for another 5 minutes. After baking, cover the croissants with a damp cloth and let them cool down a little.