Put the egg whites in a clean bowl and whisk until soft peaks form. Keep whisking and add the sugar a spoonful at a time. Fold in half of the nuts and half of the chocolate.
Spoon 8 spoonfuls on a lined baking sheet and sprinkle with the remaining nuts. Cook in a preheated oven, 140°C (275°F), Gas Mark 1, for about 1 hour. Turn off the oven and leave the meringues in the oven until they are cold.
Whip the cream and sugar to form soft peaks. Melt the remaining chocolate and fold it into the cream to create a marble effect. Use the chocolate cream to sandwich 2 meringues together and serve.