Knead the flour with the butter, sugar and sour cream. Wrap the dough in cling film and place in the refrigerator for 1 hour. Then roll out on the floured work surface and cut into small triangles with a pastry wheel or knife. When I make the cookies under the year, the triangles get a little bigger for me.
Place the cookies on a baking sheet lined with baking paper and brush with milk. Mix the sugar with the cinnamon and sprinkle on the cookies. Bake in the preheated oven on the middle rack at 200 degrees for about 10 minutes.