In a saucepan, combine the milk and salt. Scrape the seeds from the vanilla bean into the milk and add the pod, too. Put a medium-high flame under the pan.

Whisk together the eggs and sugar in a mixing bowl until lightened. Little by little, whisk in the cornstarch.

When the milk is hot enough to give off steam, temper the eggs by slowly drizzling about one-third of the hot milk into them, whisking constantly.

Pour the tempered eggs back into the saucepan and discard the vanilla bean. Cook over medium-high heat, whisking constantly until thickened, about 3-5 minutes.

When the custard starts to make big, slow "blurp" bubbles, reduce heat to medium-low and cook -- and whisk -- a minute or two more.

Remove from heat. Pour through a sieve. Stir in the butter until it's incorporated. Press a sheet of plastic wrap onto the surface of the cream and chill.