Preheat the oven to 350F and spray PAM on a 10 or 12-cup Bundt pan
In a medium bowl, whisk flour, baking powder, baking soda, salt, nutmeg, and cinnamon until well combined. Set aside.
Using a stand mixer fitted with the paddle attachment. beat butter until smooth.
Add sugars and beat on medium-high until pale and fluffy (2-3 minutes).
Reduce speed and add eggs one at a time, fully incorporating after each addition. Add rum and vanilla.
Alternate adding flour mixture and eggnog, beginning and ending with flour (3 additions of flour and 2 additions of eggnog). Fully incorporate after each addition. Do not overmix.
Spread batter evenly into prepared pan. Smooth the top with a spatula and whack the pan flatly against the counter to evenly distribute.
Bake for 45 minutes or until a toothpick inserted into the center comes out mostly clean.
Place the pan on a wire rack to cool for 10 minutes. Whack the pan flatly on the counter to loosen the cake and then turn it out on to a wire rack to cool completely.