In a medium bowl, whisk cornstarch, cocoa, and a half cup of milk.

In a medium saucepan over medium heat, combine remaining milk (1 ½ cups), Nutella, and salt, whisking until the Nutella has melted. Add in the cornstarch mixture, whisking while you pour. Bring the mixture to a boil, whisking frequently. Once the mixture comes to a boil, boil for 2 full minutes. The mixture will thicken. While boiling, alternate between whisking and scraping the bottoms and sides with a rubber spatula.

Remove the pudding from the heat and transfer to a large bowl or individual serving bowls. If you're concerned about lumps, you can pour it through a fine mesh sieve before transferring it to the bowls. Refrigerate for several hours until thickened and chilled completely.

Top with whipped cream and chopped hazelnuts right before serving.