Using an electric mixer, cream butter and sugar together. Beat in egg. Add vanilla and milk.
Mix in flour & baking powder (also add ¼ teaspoon salt if using unsalted butter).
Lay 2 pieces of plastic wrap or waxed paper on the counter.
Split dough in half. Drop half of the dough on one piece of plastic wrap & the second on the other. Shape/Roll each into a log about 2" in diameter. Wrap up & close off ends of plastic wrap. Place in refrigerator for 2 hours.
After 2 hours Preheat oven to 375 F. degrees.
Take out one log & slice into ¼" slices and place on ungreased cookie sheet. Repeat when ready to bake second log.
Bake for 10-12 minutes or until the edges are just slightly turning golden.
Recipe by THE SEMISWEET SISTERS at https://www.thesemisweetsisters.com/2018/04/14/slice-and-bake-sugar-cookies/