Combine the flour, baking powder, cinnamon and nutmeg. Set aside.
Cream sugar and butter together in mixing bowl.
Add eggnog, vanilla, and egg yolks. Beat at medium speed with a mixer until smooth.
Add the flour mixture and beat at low speed until combined. Do not over-mix.
Spoon onto ungreased cookie sheet or parchment paper and make the dough balls rather small because they will spread in the oven. I always test about 3 cookies in the oven first before making an entire batch. Sprinkle the cookies with nutmeg.
Bake 15-18 minutes, mine took 17, until the edges are lightly brown.
While the cookies are in the oven make the glaze by combining the powdered sugar with 3 T eggnog.