Prepare an ice bath and set aside.

In a medium bowl, whisk together 1/4 cup of the sugar and the egg yolks and set aside.

In a medium saucepan, combine the remaining 1/4 cup sugar, heavy cream, milk, vanilla bean (split and scraped), and salt over medium-high heat.

Bring the mixture to a simmer, stirring occasionally to prevent scorching.

Slowly pour about 1/2 cup of the hot milk mixture into the egg-yolk mixture, whisking constantly to temper the eggs.

Continue adding the hot milk mixture, about 1/2 cup at a time, until all of it has been incorporated into the egg yolk mixture.

Pour the combined mixture back into the saucepan.

Cook over low heat, stirring constantly with a wooden spoon, until the anglaise is thick enough to coat the back of a spoon, about 1-5 minutes.

Pour the anglaise through a fine-mesh sieve into a medium bowl set over the prepared ice bath.

Whisk in the Nutella, stirring occasionally, until the mixture is cool.

Cover the bowl tightly with plastic wrap, pressing it against the surface of the anglaise to prevent a skin from forming.

Transfer the covered bowl to the refrigerator and chill completely, at least 1 hour and up to overnight before serving.