Put the nuts on a piece of foil on a baking sheet, then toast under a preheated hot grill for 3–4 minutes until golden. Allow to cool slightly, then chop roughly.
Melt 75 g (3 oz) of the chocolate in a heatproof bowl over a pan of gently simmering water. Stir the butter, sugar and cream into the melted chocolate until smooth and glossy, then mix in all but 2 tablespoons of the chopped nuts.
Drop teaspoons of the mixture on to a baking sheet lined with nonstick baking paper. Chill for 2–3 hours until the mixture is firm.
Melt the remaining chocolate as before. Coat the nut clusters in the melted chocolate by holding them on a fork, one at a time, over the bowl of chocolate and spooning some of it over the top with a teaspoon. When the excess chocolate has dripped away, return the cluster to the paper-lined tray and repeat with the remainder.
Put the chocolates in a cool place and leave to set for at least 1 hour, then sprinkle with the reserved nuts. They will keep in the refrigerator for up to 4 days.