Preheat oven to 350 °F (180 °C). Line a cookie sheet with parchment paper.
In a mixing bowl, whisk flour, baking powder, salt, nutmeg, and cinnamon until well mixed.
Using an electric stand mixer, cream butter and sugars until pale and fluffy.
Add egg yolks one at a time until just combined. Add starter, extracts, and egg nog.
With the mixer set on low speed, add in dry ingredients until just incorporated, gently scraping down the sides as needed.
Drop heaping tablespoons 2" apart onto the prepared cookie sheet.
Bake for 12 minutes. Remove from oven and let cookies rest on cookie sheet for a couple of minutes before transferring to a wire rack. Allow to cool completely.
If desired, frost with Eggnog Frosting and sprinkle with nutmeg.