1 Mix together the butter, sugar, and spices: In the bowl of a stand mixer fitted with a paddle attachment, place the butter, white sugar, brown sugar, baking powder, nutmeg, cinnamon and salt.
Mix on slow speed until most of the ingredients are blended, then increase to medium speed and mix until the butter is creamy and clings to the side of the bowl, about 2 minutes.
Scrape down the sides of the bowl halfway through mixing and then afterwards.
2 Whisk liquid ingredients: In a small bowl, add the eggnog, egg yolks, vanilla, and rum extract (if using).
Beat together with a fork then drizzle the mixture into the mixing bowl as it is turned on to low speed. Continue to mix on low speed until all the liquid is incorporated. Scrape down the sides of the bowl.
3 Beat in the flour: Add the flour and turn the mixer to low. Once most of the flour has been absorbed, increase the speed…