Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, nutmeg, and cinnamon. Set aside.
2 3/4 cup (344 g) all purpose flour, spooned and leveled , 1/2 tsp baking powder, 1/2 tsp baking soda, 1/2 tsp salt, 1- 1 1/2 tsp nutmeg, 1/2 tsp cinnamon
Add the sugar and softened butter to a large bowl. Cream together with an electric mixer on high speed for 1-2 minutes until very light and fluffy.
1 cup (227 g) unsalted butter, very softened, 1 cup (200 g) granulated white sugar
Add in the egg yolks, eggnog, vanilla, and rum extract. Mix on medium speed until pale in color and very fluffy, about 1-2 minutes.
2 egg yolks, at room temperature , 1/4 cup eggnog, at room temperature (not low fat), 2 tsp vanilla, 1 tsp rum extract
Add in the dry ingredients. Mix on low speed just until combined.
Scoop the dough with a 2 tbsp cookie scoop, and roll them into balls. Then roll the dough balls in the spiced sugar.
Place the cookie dough balls at least 2 inches apart on the baking sheets. Slightly flatten each ball and form into a circle as best as you can.(See photo in the blog post above.)Bake 6-8 cookies at a time. Bake the cookies for 9-10 minutes, then let them cool on the baking sheet for 5 minutes.(When the cookies are straight out of the oven, scoot a large circular cookie cutter around them to give them a perfect circular shape.) Transfer the baked cookies to a cooling rack to finish cooling.