Making a sponge cake is the easiest thing there is to bake. Don’t let anyone tell you that it’s difficult, hard, or in any way something that only bakers can do.
The quantities and proportions for a basic cake never change. For the filling on this cake, I don’t bother to weigh as butter icing is just so easy.
If you want an absolutely perfect looking cake, you can use a sharp knife to trim round the edges and make it look perfect before sprinkling icing sugar or adding your filling.