Combine the biscuits with the cocoa, walnuts and sugar.
Melt the chocolate on a moderate stove with the milk and butter and pour this mixture into the biscuits.
Stir well and form balls the size of an apricot. Put them in the fridge to harden for 1 hour.
Melt the other chocolate and pour some over every ball.
Leave it for 1 hour in the fridge and it's ready!