Cream sugar and butter together until smooth in a different bowl. Add egg yolks, vanilla and eggnog and beat at medium speed until all the ingredients are well incorporated.
Add the flour little by little until it's incorporated to the mixture. Fold the chips into the mixture.
Drop spoonfuls of cookie dough on a greased cookie tray 2" apart from each other (you know the drill). Sprinkle some nutmeg on top of each cookie and bake for 10 to 12 minutes. Remove from oven and cool on a rack before enjoying.
Recipe by What's Cooking, Mexico? at http://whatscookingmexico.com/2009/12/17/eggnog-cookies/