In a mixing bowl add all the dry ingredients. Whisk well until everything is well incorporated. Alternatively, you can shift all the ingredients 1-2 times.
In another bowl Cream butter, Light Brown Sugar and White, until light and fluffy.
Add egg, egg yolk, vanilla Extract. Whisk until incorporated. Scarp the bottom of the pan with a spatula.
Now stir in the eggnog. Whisk until everything is mixed well.
Now add the dry ingredients in two batches. Mix well until there are no dry patches. Avoid overmixing the dough.
Cover the cookie dough with a cling wrap and chill in the refrigerator for at least 30 minutes.
Preheat oven at 190 Degree Celcius. Line a cookie tray with parchment paper.
Using a small ice cream scoop, Scoop out portions of Cookies dough and place in the lined tray 2 inches apart( the Cookies spreads while baking).
Bake 12-15 minutes in the middle rack of the oven until the top is set and sides are little crispy.
Once the cookies are baked. let it rest on the tray for 2-3 minutes. Then transfer to a wired rack. to cool completely.
While the cookies are cooling down, Make the eggnog glaze by mixing 1/2 cup icing sugar with 2 tablespoon Eggnog. The consistency should not be too watery. It should form a continuous ribbon when dropped using a spoon.
Drizzle eggnog glaze on completely cooled cookies. Sprinkle more nutmeg/Cinnamon on top if desired.