Preheat oven to 350°F. Prepare 2 baking sheets by lining them with parchment paper. Set aside.
Combine flour, baking powder, cinnamon and nutmeg in a medium bowl. Mix well with a whisk. In the bowl of an electric mixer on medium speed, cream sugar and butter until light and fluffy, about 3 minutes. Add eggnog, vanilla, and egg yolks; beat on medium speed until you have a smooth consistency. Add flour mixture and mix on low speed until combined.
Using a 1 tablespoon scoop, drop onto prepared baking sheets about 2 inches apart .
Bake for 9-11 minutes until slightly golden brown around the edges. Allow to cool on baking sheet for 2-3 minutes and transfer to a cooling rack to cool completely.
Meanwhile, prepare the eggnog drizzle in a medium bowl. Combine the powdered sugar, eggnog and vanilla. Whisking until well combined and smooth.
Drizzle over cookies and then sprinkle with fresh grated nutmeg.