Beat margarine and shortening on medium speed until soft. Add half the flour. Add sugar, egg, milk, baking powder, vanilla and salt. Mix until combined well. Add remaining flour and mix to blend well. Divide dough onto two parts and chill for 5 hours in refrigerator or two hours in freezer. Roll each half out to 1/8 to 1/4 inch thick. Cut with floured coookie cutters. Place on light colored baking sheets. Bake at 375 deg f. Bake for 7 to 8 minutes. Cookies are done when bottoms are lightly browned and edges are set. Let cookies cool for 1 minute on baking sheet. Let baking sheet cool before reusing. Cool cookies on wire rack after removing from baking sheets. Note: corn oil margarine makes a very tender cookie. Butter also works well ~ Do Not Use reduced calorie products as they are not intended for baking.