1. Preheat oven to 350°F. Line a baking sheet with parchment paper and set aside.
2. In the bowl of your stand mixer fitted with the paddle attachment mix the butter, brown sugar, and granulated sugar together for 2 minutes on medium speed. Add in the egg, yolk, vanilla extract, rum extract, cinnamon, nutmeg, baking powder, and salt. Mix for 1 minute until smooth, scraping the sides of the bowl as necessary.
3. Turn mixer to low and add in the flour, mixing until just combined.
4. Using a medium (2-tablespoon) cookie scoop portion the dough out and place it on the baking sheet 2- inches apart.
5. Bake for 9-10 minutes, or until the tops are set and the edges are lightly golden.
6. Transfer to a wire rack to cool completely.

Frost the Cookies

1. In the bowl of your stand mixer fitted with the paddle attachment, combine all the ingredients, and mix for 2 minutes until creamy and smooth, scraping the sides of the bowl as necessary.
2. Spread approximately 1 tablespoon of frosting onto each cookie.
3. Sprinkle with a little ground cinnamon and nutmeg if desired