Preheat oven to 350 degrees. Grease 2 9 inch cake pans with butter or oil.
In a large bowl, beat the butter and sugar until fluffy, about 3-4 minutes. Beat in the eggs, one at a time, until fully incorporated. Whip in the vanilla and Greek yogurt. Add the flour, baking powder, baking soda, and salt. With the mixer running, slowly stream in the eggnog and bourbon, mixing until just combined. Do not overmix.
Divide the batter evenly between the cake pans. Bake 30-35 minutes until the center is set and an inserted toothpick emerges with just a few moist crumbs. Let cool in the pans for 10 minutes, then run a knife around the edges to release the layers and flip onto a wire rack. Cool completely.
When the cakes are cooled, make the frosting. In a bowl, whip the butter, bourbon, and vanilla on low speed until combined. Add in 4 cups of powdered sugar and mix to combine, then increase the speed to medium high and whip until very light and fluffy. If needed, pour in more sugar 1/4 cup at a time until the frosting is soft and spreadable. If the frosting seems too thick, add heavy cream 1 tablespoon at a time to achieve a silky texture.
Pull out about 1 cup of frosting. Mix the yellow and blue food dyes according to package directions to achieve the desired orange hue.
Place one cake layer on a flat plate or cake stand. Frost the top generously, then add the second layer. Frost all the way around the cake until completely covered. Use a star piping tip to swizzle on some Christmas tree shapes. Place a star anise pod on top to create a Christmas star.