Finely chop 50g (2oz) of the milk or plain chocolate with the cranberries and pistachio nuts, reserving a few pieces of the nuts and the berries to decorate.
Dust a work surface with icing sugar. Roll marzipan into a rectangle 23x33cm (9x13in). Cut into 4 equal pieces. Sprinkle each with chopped chocolate and nut mixture then roll up tightly to make log shapes.
Melt remaining milk or plain chocolate in a bowl over a pan of gently simmering water (or heat in the microwave until melted). Spread over the logs and leave in a cool place to set.
Melt the white chocolate in the same way. Drizzle over the logs and decorate with pistachio and cranberry pieces. Leave to cool, cut in slices and giftwrap in transparent bags tied with ribbon. Keep for 2 weeks in an airtight container.
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