Cream butter until very soft and beat in the molasses slowly. Add the sour milk and blend. Over this mixture sift 2 cups of the flour with the soda, cinnamon and salt. Blend well. Add the rest of the flour, mixing thoroughly. This will be a stiff dough.
Roll dough about 1/3 inch thick on floured board. If it seems a little soft, place more flour on the board and roll it until it becomes firm. Cut into stars with cookie cutter.
Bake 15 minutes on greased cookie sheets in a preheated 350° oven.