Cut a 30cm length of parchment paper, ready for later.
Snap both chocolates into a medium heatproof bowl.
Either melt in the microwave in 30 second blasts, stirring between each go, or over a pan of simmering water, shallow enough that the water doesn’t touch the bowl.
When melted, remove from the heat.
Break the biscuits into small chunks, adding to the melted chocolate as you go.
Add the chopped nuts, fruits, orange zest and stem ginger, if using, and stir until everything is evenly coated.
Spoon the mixture into an 18cm-long sausage shape in the centre of the parchment.
Roll the paper up to wrap the mixture, shape it into a neat sausage of even thickness, retaining this length, and twist the paper ends to secure.
Lift onto a tray and leave to cool for 30 minutes, before chilling in the fridge for 1-2 hours until set firm.
Unwrap and slice into 12 biscuits, about 1.5cm thick, using a knife dipped in hot water and then wiped.
If it is too crumbly to slice, leave it to come to room temperature and then try cutting again for a cleaner finish.