In a large bowl or stand mixer, cream together butter and sugars.
Beat until light and fluffy.
Mix in egg, followed by vanilla.
Scrape bowl as needed.
Mix in salt, spices, baking powder and cream of tartar.
Add one cup of flour at a time, increasing speed after each addition.
Lastly, slowly add in eggnog, mixing until just combined and no streaks remain.
Chill dough for 1-2 hours or until dough is firm but manageable.
Preheat oven to 350°F.
Line a baking sheet with a silicone baking mat or parchment paper.
In a small bowl, combine sugar, nutmeg and cinnamon.
Using a small cookie scoop, scoop slightly heaping balls of dough.
Shape into smooth 1-inch balls.
Roll each dough ball into sugar mixture.
Space 2-inches apart on prepared baking sheet.
Bake for 12-14 minutes.
Transfer cookies to a wire rack to cool completely.
Store cookies in an airtight container.