Whisk together the flour, cornstarch, baking powder, cinnamon, nutmeg, and salt in a medium bowl.
In a separate large bowl, whisk together the butter, eggnog, and vanilla. Then, whisk in the granulated and brown sugars.
Slowly fold in the flour mixture lightly. Cover the bowl and chill the cookie dough for 1 hour.
Preheat the oven to 350°F degrees. Remove cookie dough from refrigerator.
Line baking sheet with parchment paper.
Stir together the sugar, cinnamon, and nutmeg in a small bowl.
Using a small cookie dough scoop. Place one ball of dough into your hand and roll into the sugar mixture. If desired, roll again to make sure the ball is coated well. Place sugar coated dough ball on baking sheet. Repeat until you've used all the dough.
Bake the cookies at 350°F for 11 minutes. After 2 minutes, transfer to cooling rack to cool completely.