Place chocolate in a large mixing bowl. Place cream in a saucepan and bring to the boil, then immediately pour over chocolate. Mix until chocolate has melted. (This is called a ganache.) Set aside at room temperature, covered, for 1-1 1/2 hours to cool completely and until set. Use a teaspoon to spoon out bite-sized pieces. Dust your hands with a little icing sugar to prevent them sticking and roll mixture into balls in the palm of your hands. Roll in cocoa; serve with coffee.