For the vanilla sauce, first empty the milk and whipping cream into a small saucepan.
Cut the vanilla bean lengthwise, scrape out the pulp and add both to the milk and whipped cream mixture. Bring everything to a gentle boil.
In the meantime, whisk the egg yolks, egg, sugar and salt in a bowl until the sugar dissolves.
When the mixture boils, pull the saucepan off the stove and whisk a little of the hot liquid into the egg mixture. Next, run all of the egg mixture into the hot milk while stirring, return the saucepan to the kitchen stove and stir until the sauce thickens. Do not boil under any circumstances or the sauce will curdle.
Pour the custard through a sieve into a large enough bowl and leave to cool.