Preheat oven to 350 degrees.

In a large bowl, cream together the butter and 2 cups sugar until light and fluffy. Beat in the egg and vanilla.

In a large bowl, sift together the flour, cream of tartar, baking soda and salt.

Add the flour mixture to the creamed mixture, alternately with the eggnog. The dough will be thick and slightly sticky.

Mix together 1/3 cup sugar and 1/2 teaspoon ground nutmeg in a small bowl.

Shape the dough into rounded tablespoons; roll in sugar and nutmeg mixture. Place 2 inches apart on ungreased baking sheets and bake for 8-10 minutes, or until cookies are just set and starting to crack.