Eggnog Sponge Cake with Eggnog Frosting

My version of a frosted single-layer sponge cake using eggnog instead of milk, adapted from Hot-Milk Sponge Cake in THE FANNY FARMER BAKING BOOK by Marion Cunningham, and informed by America's Test Kitchen. :) SOME NOTES: a. If you don't have cake flour, you can use all-purpose, but the crumb or texture of the cake will be coarser and the cake may not rise as much. b. If you don't have any eggnog, you can use milk. Just add ⅛ teaspoon each of cinnamon and ginger and ¼ teaspoon of nutmeg to the flour in step #3 for flavor. c. If you don't have parchment paper, you can use waxed paper in a pinch but it doesn't peel off as well. YOU MUST LINE THE BOTTOM OF THE PAN OR CAKE WILL STICK! d. The recipe can be doubled if you want to make a two-layer cake. If you want to make a tube or sheet cake, the baking time will be longer but I can't give you any insight into it since I've only made it as the recipe is written.