Line a tray with baking parchment. In a small saucepan, bring the tonic to the boil and reduce by half. Set aside to cool.

Gently heat the cream and butter in a saucepan until the butter has melted. Put the chocolate in a heatproof bowl and pour over the hot cream, gently stirring until the chocolate has melted. Stir through the gin and tonic and refrigerate for 10 mins or until firm enough to scoop into mounds.

With two teaspoons form the mixture into 12 walnut-sized mounds, place on the tray and refrigerate for an hour. Use your fingers to gently smooth each one into a ball and freeze for 30 mins.

Put the white chocolate into a microwaveable bowl and blast for 30 seconds at a time until melted. Stir through the lemon zest and half of the lime zest. Allow to cool a little. Drop each frozen truffle into the melted chocolate, turning it over with a fork to coat. Place on the tray, finishing with an extra grating of lime zest. Repeat for the remaining truffles and freeze for 10 -15 mins until set. Store in the fridge for up to 3 days.