In a medium-sized bowl, whisk together the flour, baking soda, salt, nutmeg, and cinnamon. Set the bowl aside.
In the bowl of a stand mixer, cream together the butter and sugars until light and fluffy. Add the bourbon, egg, and and eggnog. Beat until combined. Scrape the sides of the bowl as necessary.
Bit by bit, add the flour mixture and mix until combined. Again, scrape down the sides of the bowl as needed.
Refrigerate the cookie dough for at least 3 hours.
Scooped the dough, using a ~1.5 tbs cookie scoop, onto parchment paper-lined baking sheets.
Preheat the oven to 350 degrees F. Bake 9-11 minutes or until the cookies are golden around the edges.
Remove the cookies from the oven and allow them to cool on the baking sheets for 5 minutes before removing them to a wire rack to finish cooling completely.
Combine the powdered sugar, bourbon, and eggnog in a small bowl. Stir until the glaze comes together.
Drizzle over the cooled cookies and top with some freshly grated nutmeg and/or colored sanding sugar, if desired.