Make a yeast dough from flour, yeast, sugar, egg and butter and let it rest. Divide the dough and roll out both halves into a round shape. Now divide into triangles with the help of a cake divider. Roll up the triangles into croissants. Mix the egg yolk and milk and brush the croissants with it. At the end, sprinkle the croissants with granulated sugar and bake in the oven at approx. 200 ° C for 10-20 minutes.