Bring a little water to a simmer in a pan. Place the chocolate and butter in a large bowl, then set the bowl over the simmering water. (Do not allow the base of the bowl to touch the water.) Stir until melted and glossy.
Heat the cream in a separate saucepan until almost boiling (but do not allow the cream to reach boiling point).
Pour the hot cream over the melted chocolate and mix together until smooth and well combined. Stir in a pinch of salt.
Line a roasting tray with greaseproof paper and pour in the melted chocolate. Set aside to cool, then chill in the fridge until set.
Once the chocolate mixture has cooled and set, mix the chopped nuts together and sprinkle onto a baking tray.
Roll the chilled chocolate mixture into small balls using your hands, then roll each ball in the chopped nuts until completely coated. Place the truffles onto a baking tray or plate and chill until ready to serve.