Cream margarine with sugar; add eggs one at atime, beating well after each addition.
Sift flour with salt and baking powder. Add to butter mixture alternately with milk. Add vanilla.
Dough should be firm but soft.
Chill overnight or several hours.
Break off small pieces and roll thin. (Keep remainder chilled while working.) Cut with cookie cutter and bake on cookie sheets at 350° for 10-12 minutes. Ice, if desired.