Preparations: Preheat the oven to 180C/350F.Line a two 20 cm springforms with parchment paper.
In a mixing bowl, whisk butter and sugar using the electric whisk. Add the eggs one by one and vanilla extract, whisk. Next, add the eggnog, whisk. Then, stir in the flour, baking powder, nutmeg, and cinnamon.
Distribute the batter equally between the two springforms. Bake for 30 minutes.
Making the eggnog buttercream
In a mixing bowl, beat the butter well until it becomes creamy. Add the powdered sugar and eggnog and beat again until the mixture becomes soft.
Assembling the Cake
Spread some of the eggnog buttercream on top of the first cake then top it with the second cake. Now, spread the rest of the eggnog buttercream on top of the second cake and all the sides.
Sprinkle the white chocolate on top of the cake. Use some of the buttercream to make bulbs on the sides of the cake. Top the blubs with some cinnamon or sprinkles if you want.