Preheat oven to 350°F (177°C). Line two cookie sheets with parchment paper or silicone baking mats. Set aside.
In a medium bowl, whisk together the flour, baking powder, salt, nutmeg and cinnamon. Set aside.
In a large mixing bowl or the bowl of a stand mixer, cream together the butter and sugar until pale in colour and fluffy (about 2 minutes), scraping down the sides of the bowl as needed.
Add the eggnog, vanilla and rum extract and stir to combine. Add the egg yolks one at a time, and mix on medium speed until well combined.
Adjust mixing speed to low and add in the flour, mixing until just combined and no flour streaks remain.
Using a 1.5 tablepoon size cookie scoop (or up to 2 tablespoons), scoop out the dough and place on the prepared cookie sheet. Leave about 4 inches between each cookie.
Bake for 12 minutes or until the edges are set and cookies look golden. Allow cookies to cool on cookie sheet for 10 minutes before transferring to a wire rack to cool completely.