Whisk the whipped cream with the cold milk until it thickens. Separate the whites and yolks of the eggs. In a bowl, whisk the egg yolks together with the granulated sugar until frothy. In another bowl, whisk the egg whites with a pinch of salt until it turns into snow. Add the egg whites, then the yolks, and whisk them with a mixer.

Put chunks of wafer and biscuit on top. After adding the hazelnuts, mix all the ingredients. Spread plastic wrap in a deep glass bowl or cake tin and pour the mixture into it. Press it well with a spoon and leave it in the freezer until frozen.

For the sauce, mix the flour, starch, cocoa and powdered sugar in a saucepan. Add milk and water on it. Put the pot on the stove and cook it by stirring until it reaches an eye.

Remove the pan from the heat and cool. Add margarine and beat with a mixer for 2 minutes. Before serving, remove the frozen parfait from the freezer and turn it upside down on the serving plate. Take the plastic wrap on it. Pour the sauce you have prepared and serve without waiting.