Butter should not be 100% melted and it is fine to see a small amount of soft, unmelted butter.
Eggs should be room temperature.
Batter should be mixed until there are no lumps, whether it be 2 minutes or 5 minutes.
Because some people have nut allergies or don't like nuts, rather than adding them into the batter, they can be served on top of the whipping cream on individual servings.
Grease the cake pan well.
Cool the cake on a baking rack, so the bottom (which becomes the top) doesn't become soggy and the top (which becomes the bottom), will flatten.