First, in a medium bowl, whisk together flour, baking powder, salt, nutmeg and cinnamon. Set aside.
In the bowl of an electric stand mixer (or using a hand mixer), mix butter, granulated sugar and brown sugar until light and fluffy, about 3 minutes.
Next, add egg yolks one at a time, mixing just until combined.
Add vanilla extract, rum extract and egg nog and mix until incorporated.
With mixer set on low speed, slowly add in dry ingredients and mix just until combined (avoid over mixing).Then, cover and chill cookie dough for 30 minutes and up to 48 hours.
Preheat oven to 350°F. Line a baking sheet with parchment paper. Scoop dough out by heaping tablespoonfuls, gently roll into a ball and place on prepared baking sheet. Space cookies 2-inches apart.
Bake in preheated oven for 11 to 13 minutes. Cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely. Prepare the frosting. Swipe up for the instructions!
Use an offset spatula to spread frosting on cooled cookies. Sprinkle lightly with nutmeg if desired. Enjoy!