Preheat your oven to 325°F (163°C) and grease your two 8-inch round cake pans with butter or oil, then dust with flour.

In a large mixing bowl, whisk together the cake flour, granulated sugar, baking powder, salt, nutmeg, and cinnamon.

In a separate bowl, whisk together the eggnog, milk, vegetable oil, vanilla bean paste, rum extract, and eggs until smooth.

Add the chunks of unsalted butter to the dry ingredients and mix on low speed until it resembles coarse crumbs. Then add the wet ingredients and mix until just combined.

Pour the batter evenly into the prepared pans and bake for 50-55 minutes until a toothpick inserted comes out clean.

Let the cakes cool in the pans for about 10 minutes, then invert onto a wire rack to cool completely.

In a mixing bowl, beat the unsalted butter until fluffy, gradually add confectioner's sugar until combined.

Pour in milk and eggnog while beating on medium speed until achieving a creamy consistency.

Once the cakes are cooled, place one layer on a serving platter and spread eggnog buttercream on top, then place the second layer and frost the top and sides of the cake.

Decorate with additional spices or festive garnishes if desired.

Slice and serve the cake with coffee or tea.