In a medium bowl whisk together the flour, baking powder, salt, cinnamon and nutmeg then set aside.
Cream the butter and sugar in the bowl of your stand mixer fitted with a paddle attachment or in a large bowl if using an electric hand mixer. Scrap the bowl down and beat on high until light and fluffy.
Pour in the eggnog and vanilla then add the egg yolks in one at a time while mixing on medium then scrape the bowl down and mix once more.
Add the flour in while mixing on low and mix until just combined. Finish the batter off with a spatula mixing in any stray bits of butter or flour.
Portion out roughly two-tablespoon sized pieces of dough (40g) and drop them onto a parchment or silicone-lined baking sheet leaving about 4 inches of room between each. You can roll each ball in your hands for a more finished look but this is optional. Bake in the center rack at 350F for 11-12 minutes or until the edges are set and the center appears dry.
While the cookies are baking mix the glaze up. Add a cup of powdered sugar to a medium bowl along with the cinnamon and nutmeg then drizzle in 3 tablespoons of eggnog and 1 tsp of vanilla. Whisk together adding a tablespoon at a time of eggnog as needed to achieve a drizzling consistency.
Drizzle the icing onto the cooled cookies and enjoy.
Notes
No chill time is needed but you can chill the dough if making it ahead of time.
Measure your flour with a scale for best results. If you don't have one luff the flour and sprinkle it into your measuring cup before leveling.
Try to keep your cookies all the same size so they bake evenly. Make sure you don't use more than 2 tbsp of cookie dough or the cookies will spread too much.
Make sure to let the cookies cool on the baking tray for around 10 minutes before moving to a cooling rack.
You can add rum or bourbon to your eggnog for added depth of flavor or use 1/2 tsp rum extract for a similar effect.
You can make the glaze while the cookies are baking to save time.