Place the chocolate and butter in a large heatproof bowl set over a large pan of gently simmering water. Make sure the bottom of the bowl does not touch the water. Heat gently until melted.
Heat the cream in a separate medium saucepan until warm. Pour the cream over the melted chocolate mixture, add the salt and stir until smooth.
Pour the mixture into a baking tray lined with baking paper and refrigerate until set. This will take at least an hour.
Once set, remove from the tin and roll teaspoonsful into balls. Roll in the cocoa powder and then in the chopped nuts. Enjoy!
The chocolate truffle mixture can be frozen as a block in the tray.
You can add a little more sea salt and maybe some caramel sauce to make salted caramel truffles.
You can flavour the cream with vanilla, cinnamon sticks, dried chilli or any other whole spices, when warming.