1-First Steps: Mixing the Dough: In a stand mixer with a paddle attachment, beat the unsalted butter and sugars until light and fluffy, about 3 to 4 minutes, scraping the bowl as needed. Mix in the dark rum and vanilla extract for 30 seconds, then add the eggs and yolks and beat until fluffy, about 2 minutes. In a separate bowl, whisk together the all-purpose flour, cream of tartar, baking powder, kosher salt, ground cinnamon, and freshly ground nutmeg.

2-Combining and Chilling: Gradually add the dry ingredients to the mixer on low speed, followed by the eggnog, until the dough begins to clump. Portion the dough using a 2-ounce scoop onto a parchment-lined baking sheet and cover with plastic wrap to chill for 1 hour.

3: Preheat the oven to 350°F and prepare the sugar coating by combining granulated sugar, ground cinnamon, and freshly ground nutmeg in a small bowl. Roll the chilled dough balls in this mixture to coat thoroughly, then place them on a parchment-lined baking sheet with 2 to 3 inches of spacing. Bake one tray at a time for 15 to 17 minutes until the edges just start to turn golden and the centers are puffy, then cool on a wire rack before serving.