Heat chocolate and water in double boiler. Add beaten egg yolks and sugar. Stir until thickened. Cool. Add 1/2 pint of whipped cream, egg whites (beaten stiff), vanilla, marshmallows, and pecans. Butter a 8" baking dish and cover the bottom with a layer of crushed vanilla wafers. Over this, place a  layer of the chocolate mixture, then another layer of crushed wafers. Repeat the layers one more time. Refrigerate overnight. For serving, cut into squares and top with whipped cream. Serves 12-16