Preheat your oven to 325°F (163°C) and grease and flour two 8-inch round cake pans.

In a large bowl, whisk together the dry ingredients: cake flour, granulated sugar, baking powder, salt, ground nutmeg, and ground cinnamon.

In another bowl, mix the wet ingredients: eggnog, milk, oil, vanilla bean paste, rum extract, and eggs until smooth.

Add cold butter cut into chunks to the dry ingredients and mix until it resembles coarse crumbs.

Gradually combine the wet mixture with the dry mixture, mixing until just incorporated.

Divide the batter between the two prepared pans and bake for 50-55 minutes or until a toothpick comes out clean.

Cool for 10 minutes in the pan, and then transfer to a wire rack to cool completely.

For the frosting, beat the unsalted butter until fluffy, then gradually add confectioner's sugar and milk until smooth.

Once cooled, frost the cake layers with eggnog buttercream, applying a generous layer between the cakes and around the sides.