For the croissants, first prepare the yeast dough the night before. Crumble the yeast into the lukewarm milk and mix with sugar. Sift the flour into a bowl and make a well in the center. Pour the yeast mixture into the well. Add eggs, 50 g butter and salt and mix well. Leave in the refrigerator overnight.
The next day, remove the dough from the refrigerator and roll out into a square on a work surface. Roll out the butter between plastic wrap also to half the size of the square. Dust the butter with flour and place it in the center of the yeast dough so that a triangle can be formed over the butter on all 4 sides.
Now roll out the dough into a rectangle, fold the rectangle over three times and roll out again into a rectangle. You should repeat this process 2 or 3 times. Cut triangles out of the rectangle and roll them into croissants from the wide side. Preheat the oven to 220°C. Place the croissants on a baking tray lined with baking paper and bake for about 15 to 20 minutes. Allow to cool slightly and brush the croissants with butter or jam.