To caramelize the sugar: put it in a smooth iron or aluminum saucepan over low heat and stir constantly until the sugar is melted and smoking, 8 to 10 minutes. Remove from the heat; add the boiling water slowly stirring as you add to prevent lumps. Return it to the heat and cook 8 to 10 minutes more, to a rich brown. This syrup hardens on standing but can be melted over hot water.
To make the pudding: scald the cream, mix with the sugar and pour into the egg yolks, stirring slowly. Add the canilla and beat slowly until well blended and cooled. Whip the egg whites stiff and add to the custard.
Put half of the caramel in a pudding mold or casserole; tilt it so as to coat the bottom and sides. Pour the custard in and set it in a pan of hot water. Bake in a moderate oven (325°F.) 20 to 30 minutes or until firm. Let the pudding cool in the baking dish, preferably overnight.
Turn it out on a round serving dish. Garnish with a sauce made of the other half of the caramel melted over hot water. Ad to it 2 tablespoons cognac and 1 cup of cream whipped stiff.