In a stand mixer, beat butter and 1 cup sugar until light and fluffy, about 30-45 seconds.
Add baking soda, cream of tartar, egg, eggnog and vanilla and beat again until evenly incorporated. Scrape down side of the bowl.
Add flour and beat on low speed until the mixture is evenly incorporated and the dough becomes somewhat clumpy.
Cover with plastic film and refrigerate for at least 30 minutes up to 24 hours.
In a small bowl mix together 2 tablespoons sugar and cinnamon. Roll dough into 1" balls, then roll into sugar mixture.
Place on ungreased cookie sheet and flatten slightly.
Bake in a 375 degree oven for 10-11 minutes.
After removing from oven, (again) slightly flatten the cookie's "dome" and allow to sit on cookie sheet for exactly two more minutes. Transfer to solid surface to cool.