Prepare an ice bath; set aside. In a medium bowl, whisk together 1/4 cup sugar and egg yolks; set aside.

In a medium saucepan over medium-high heat combine remaining 1/4 cup sugar, heavy cream, milk, vanilla bean with scrapings, and salt. Bring just to a simmer. Using a measuring cup or a ladle, slowly pour about 1/2 cup of the hot milk mixture into the egg-yolk mixture. Whisking constantly, continue to add milk mixture, about 1/2 cup at a time, until it has all been added. Pour mixture back into saucepan.

Cook over low heat, stirring constantly with a wooden spoon, until thick enough to coat back of a spoon, 1 to 5 minutes. Pour through a fine-mesh sieve into a medium bowl, set over ice bath. Whisk in Nutella; stir occasionally until cool.

Cover, and transfer to refrigerator until completely chilled, at least one hour and up to overnight.