Preheat oven to 350°F (180°C). In a mixing bowl, whisk together flour, baking powder, salt, nutmeg and cinnamon for 30 seconds, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment, whip together butter, granulated sugar and brown sugar until pale and fluffy.
Mix in egg yolks one at a time, blending just until combined after each addition. Mix in vanilla extract, rum extract and egg nog. With mixer set on low speed, slowly add in dry ingredients and mix just until combined.
Scoop dough out by the heaping tablespoonfuls and drop onto Silpat or parchment paper lined baking sheets, spacing cookies 2-inches apart.
Bake in preheated oven 11 - 13 minutes. Allow to rest on baking sheet several minutes before transferring to a wire rack to cool. Cool completely then frost with Eggnog Frosting and sprinkle tops lightly with nutmeg.
For the Eggnog Frosting:
In the bowl of an electric stand mixer fitted with the paddle attachment, whip butter until very pale and fluffy. Add in rum extract and 3 Tbsp eggnog and mix in powdered sugar. Add additional eggnog to reach desired consistency.
Cookies previously listed 2 1/4 cups flour (spooned and leveled method) when using the easier scoop and level method this is only 2 cups to equal the same amount. If you'd like cookies to be a little thicker you can add 2 extra tablespoons of flour.