Melt the chocolate in bain-marie; add limoncello. Stir frequently as white chocolate tends to burn easily.
Heat the cream till nearly boiling then add to the melted chocolate. Stir until thick and velvety. Stir in the lemon zest. Leave to cool in the fridge for 2-3 hours, or until firm enough to work with.
Line a baking tray with non-stick paper. Wearing disposable gloves, scoop a teaspoon of the truffle mixture and roll into balls using the palms of your hands. If the mixture is a bit sticky, dust with icing sugar. Place each rolled truffle on the baking tray; return to the fridge and allow to firm up.
To coat the truffles; use a fork or skewer to dip each truffle into melted white chocolate then return it to the baking tray to set.
Pipe or drizzle some melted dark chocolate across the top of each truffle.
When all the truffles are made, place them back in the fridge for a couple of hours before packing them into cellophane gift bags or chocolate boxes.