Heat the oven to 180C/fan 160C/gas 4. Butter a non-stick baking tin (about 31 x 17 x 3.5cm) or line the base if you prefer. Break the chocolate into a saucepan, add the butter, sugar and juice or milk, then warm gently, stirring frequently until melted and evenly mixed. Allow to cool slightly, then beat in the eggs one at a time. Fold in the flour, cinnamon and cranberries.
Spread half the mixture into the prepared tin, scatter over the nuts, then gently spread the rest of the mixture on top. Bake for 25-30 mins. Cut into squares while still warm. Will keep in an airtight container for up to a week.