Preheat the oven to 325 degrees.
Grease and flour two 8" round cake pans.
In a mixing bowl, combine the flour, sugar, baking powder, salt, nutmeg and cinnamon. Whisk well.
In another bowl, combine the eggnog, milk, oil, vanilla bean paste (or extract), rum extract and eggs. Mix well with a whisk and set aside.
Cut your almost room temperature butter into chunks. Turn your mixer on low and add in the butter slowly to your dry ingredients. Mix on medium until all the flour is coated with the butter and the mixture is crumbly with a sand-like texture.
Pour in about a third of the liquid mixture. Mix on low to medium until combined. About 30 seconds.
Pour in the last of the liquid mixture and mix again until combined. Don’t overmix the batter. You don't want to mix for several minutes. Only mix until the ingredients are well combined.
Use a rubber spatula and scrape the sides of the bowl. Mix again for only about 10 to 15 seconds.
Pour into prepared pans and bake for approximately 50-55 minutes.
Cake layers are done when the sides start pulling away from the pan and a toothpick inserted into the middle comes out with a few crumbs still on it.
Set the cake pans on wire racks to cool for ten minutes, then turn the cakes out onto the racks and let them cool out of the pans completely before adding the buttercream.