Grate the marzipan (this is made more effortless if you put it in the fridge for half an hour first).
Place the marzipan, cake, jam, rum and cocoa powder either into a food processor or a stand mixer with the beater attachment.
Mix/whizz until the mixture becomes a smooth paste; to start with, you will think “oh, that’s never going to work,” then all of a sudden the ingredients will change from a crumby mess to a glorious chocolate squidge.
Now is the ideal moment to scoop out a sample and invite family members to air their opinion regarding the blend of flavours, and add more cocoa or marzipan accordingly (I always plump for the “it needs more rum” option).
Once everyone is happy, pop the mix in the fridge for half an hour to let it firm up a little.
Form into balls (about 15g or the size of a small walnut) then roll them in either chocolate vermicelli or sieved cocoa for a darker, more adult palate.
Place in petit-four cases and serve. The romkugler will last about a week in an airtight tin, but can be made ahead of time and stored in the freezer for a month if you have used fresh cake/pastry.