Add 2 1/2 cups milk, sugar, salt, and vanilla bean to a medium saucepan.

Heat over medium heat until it comes to a simmer.

Add cornstarch, flour, egg yolks, and remaining 1/2 cup milk to a large bowl. A large pitcher is a perfect tool for the job. This recipe involves some pouring, so it is less mess.

Whisk the yolk mixture until combined.

When the milk mixture is hot, ladle into the yolk mixture, whisking constantly. This will temper the eggs and you will avoid having scrambled eggs.

Slowly add in the rest of the hot milk.

Pour it all back into the saucepan.

Return to medium heat. Bring to a boil, stirring constantly.

When it starts to bubble, cook for an additional 30 seconds. It may look like it going to curdle, but keep stirring, it will all work out, I promise.

Pour through a sieve to get out any little pieces of cooked egg, and to ensure a super smooth creme pat.

Add the butter, and vanilla extract if you are using that.

Stir until silky and smooth.

Cover with plastic wrap that touches the surface of the custard. This will keep it from getting a film. Let cool a bit, then put in the fridge to chill, about 2 hours.

Whip the cold heavy cream to medium peaks.

Fold a few spoonfuls of the custard into the cream.

Gradually add the rest of the custard, being careful to not knock the air out.