Place the baked cake upside down on a thick baseboard and brush with boiled, sieved apricot jam.
Knead the marzipan to the right size and about 5mm thick. Cover the cake with the marzipan and use yours hands to smooth down the top and sides, pricking any air bubbles with a pin.
Remember to keep all utensils dry otherwise the moisture will dissolve the sugar leaving craters.