In a medium bowl, sift together flour, cream of tartar, baking soda, and salt. In the bowl of an electric mixer fitted with a paddle attachment, beat butter and ½ cup sugar on medium speed until light and fluffy, about 2 minutes. Beat in egg and eggnog, then beat in dry ingredients until just incorporated. Cover dough and chill 1 hour.
Preheat oven to 350 F. In a small bowl, mix 2 tablespoons sugar with the cinnamon and nutmeg. Scoop a tablespoon of dough and roll in the sugar and spice mixture. Place 2 inches apart on baking sheets.
Bake 10 to 12 minutes, or until cookies are just set in the center. Let cool 5 minutes before transferring to wire rack to cool. Store in an airtight container for up to a week.
Cookies may be fluffier or chewier, depending on eggnog brand.
Per serving: 74 calories, 2 grams fat (1 gram saturated fat), 12 grams total carbohydrates, 15 milligrams cholesterol, 47 milligrams sodium, 0.5 grams fiber, 1 gram protein.
