Preheat oven to 350 degrees.
In a medium bowl, whisk together flour, baking powder, salt, nutmeg and cinnamon. Set aside.
In a large bowl, using an electric hand mixer or a stand mixer, whip together butter, sugars until fluffy.
Mix in egg yolks one at a time until combined after each one. Mix in vanilla and eggnog.
With mixer on a low speed add 1/2 flour and mix until just combined. Add the last of four and mix until thoroughly combined.
Using an ice cream scoop, place cookie dough about 2" apart onto a cookie sheet lined with parchment paper, a Silpat, or lightly spray with a cooking spray.
Bake for 11-13 minutes until lightly browned.
Allow cookies to rest on baking sheet for a few minutes and then transfer to a wire rack to cool.
While cookies are cooling, make the eggnog icing.
In a medium bowl mix together butters, powdered sugar, vanilla and eggnog to desired consistency.
Dip cookies top side into icing, or drizzle icing onto cookies. Sprinkle ground nutmeg onto top of cookies. Let set.
Enjoy.
