The parfait portion of this recipe is, of course, optional, but if you like eggnog even a little, it's a fun way to take this seasonal treat to the next level. Plus, since the cake, itself, isn't too sweet, the eggnog isn't quite as over the top as you'd expect.
Regarding the cakes: I've only ever made these in paper loaf pans and suspect that, if you use metal pans, you may be able to decrease the baking time. You can also bake a single cake in one (1) 1.5 quart loaf pan, though, again, you may have to adjust baking time accordingly.