Pour the cream into a heavy-based saucepan and add the chocolate. Heat gently, stirring occasionally, for about 4–5 minutes, until the chocolate has melted. Allow to cool.
Whisk the cream mixture until thick, then chill in the refrigerator for 3–4 hours.
Put the peppermints into a plastic bag, crush them with a rolling pin, then stir into the chilled cream mixture. Drop teaspoons of the soft mixture on to a plate and chill for 1 hour or freeze for 30 minutes until firm.
Sprinkle the icing sugar on to another plate, then roll the truffles in the sugar to form neat balls. When packed in the gift box, dust with the remaining sugar. Chill for at least 2 hours before using. The truffles will keep in the refrigerator for up to 4 days.