Butter a bowl and line with the roasted and chopped nuts (1). Mix caster sugar and butter, add egg yolks slowly. Add grated chocolate and ground nuts (2). Beat egg whites until stiff and gently fold into mixture. Turn into the lined bowl. Cover with a double layer of greaseproof paper with a folded pleat down the centre and tie firmly with string. A double strip of kitchen foil laid under the bowl and projecting up the sides will make lifting it out easier. Place bowl in a large saucepan 3/4 full of water and steam for 2 hours. Carefully turn out on to a serving plate. Just before serving, pour over some of the lightly whipped cream. Serve the remaining cream separately.