The easiest way to get a smooth finish is to apply a fairly thick layer of fondant over marzipan. You don’t have to use marzipan (brush the cake with sieved and warmed apricot jam instead), but ...

Apply a little water to the top of the ... Trim round the bottom edge of the cake, discarding the excess fondant. Wipe a little water on the top of your covered cake so it forms a tacky surface ...