Cream butter; add sugar and cream well. Add beaten eggs and molasses, mix. In a separate bowl, sift flour, baking soda, and spices together. In another bowl, mix together sour cream and cream of tartar. Alternately add flour mixture and sour cream mixture to the creamed butter/sugar/molasses mixture. Add enough of the flour to make a soft dough; chill. Roll out dough and cut with large round cookie cutter. Bake cookies on a greased pan in a 350-degree oven for 15–20 minutes. If cookies are cooled, have the liquid for the frosting hot. Stir the liquid into the sifted powdered sugar, adding a few drops at a time, as needed. The icing is of the proper consistency when it coats the spoon.