Combine flour, baking powder, cinnamon and nutmeg.
Cream sugar and butter until light.
Add eggnog, vanilla, and egg yolks; beat at medium speed with mixer until smooth.
Add flour mixture and beat at low speed until just combined. Do not overmix.
Drop by teaspoonfuls onto ungreased cookie sheet 1 inch apart.
Sprinkle lightly with nutmeg.
Bake 15-18 minutes until bottoms turn light brown.
While cookies are in the oven,make the eggnog glaze by whisking together the powdered sugar with the three tbsp of eggnog. I sometimes make the icing the night before.
Let cookies cool for five minutes, glaze and sprinkle with cinnamon.
Place in the fridge for 15 minutes to harden the icing a bit.
Notes
adding a pinch of nutmeg to the glaze is my favorite addition
if you make the cookies larger, bake them 20-22 minutes