My mom makes these every Christmas and sometimes for other holidays. They're soft and moist! Cook and prep time are approximate and don't account for chill time.
- Allow butter to soften (not melt!) at room temperature. In a large bowl, cream butter and sugar.
- Add egg, vanilla, cream of tartar and baking soda.
- Add flour alternately with milk.
- Cover with plastic wrap and chill for at least an hour in the refrigerator. (I usually chill it overnight.).
- Preheat oven to 350°F.
- Roll out with plenty of flour to keep from sticking, but try to avoid incorporating too much flour into the dough since it will make the cookies less moist.
- Cut out into circles or with your choice of cookie cutters. Carefully transfer cookies to an ungreased cookie sheet.
- Bake on a cookie sheet in the oven until they become a light gold color. Watch them carefully so that they don't get overdone.
- Allow to cook completely before icing.
- For icing, put a couple of tablespoons of not-quite-boiling water into a large bowl. Add the confectioners' sugar and mix together, adding more water as you need to form a thick paste. Color, as desired.
- Spread about 1 tablespoon of icing on each cookie. Decorate with colored sugar and sprinkles as desired.