Start by breaking up the cake into small pieces and gently rubbing these pieces between your fingers and thumbs to create crumbs. Add the chopped nuts and stir in

Using electric beaters, cream together the butter, cocoa powder, icing sugar, milk and rum (if using). You will end up with a soft, smooth buttercream

Divide the mixture into 8 portions. Roll one of these portions into a ball, allowing the heat from your hands to soften the edge of the ball slightly before rolling it in the chocolate strands (it helps them to stick). Once generously covered, place the ball into a paper case and continue to roll the rest of the balls. Allow the balls to firm up in the fridge for several hours. Remove approximately 1 hour before serving to take the chill off of them

Any remaining truffle balls can be stored in an airtight container in the fridge for up to 3 days