First put a saucepan with the milk and vanilla extract on the fire and bring to the boil.
In the meantime, mix the cornstarch with the sugar in a bowl.
Pour the hot milk flush, stirring vigorously with a whisk or, even better with the electric whisk to prevent lumps from forming.
Put the pan back on the heat and, stirring constantly, cook over low heat until the cream has thickened.
Pour into a bowl and cover with contact film and let cool.
Whip the cold cream from the fridge and add, a little at a time, to the now cooled cream, mixing from bottom to top.
Put the cream in a sac-à-poche and put in the fridge until it is used.