Preheat the oven to 250˚ F. Place the hazelnuts on a rimmed baking sheet. Bake for 20 minutes until lightly toasted and the skins have cracked. Transfer the hazelnuts to a clean kitchen towel. Fold half of the towel over the top of the hazelnuts and roll them around gently to help remove the loosened skins. Transfer the skinned hazelnuts to a cutting board and chop coarsely.
Line an 8 x 8-inch baking pan with foil and grease lightly with butter. Set a heatproof bowl over a pot with a few inches of simmering water (do not boil). In the bowl, combine the sweetened condensed milk, vanilla, chocolate, Nutella, butter, and salt. Heat, stirring occasionally, until the mixture is fully melted and smooth.
Remove the bowl from the heat. Add the toasted hazelnuts and dried cherries to the bowl and fold in until evenly combined. Pour the mixture into the prepared baking pan and spread into an even layer. After it has cooled for a few minutes, sprinkle lightly with additional sea salt. Cover and refrigerate until firm, about 3-4 hours.
Use the foil to lift the fudge from the pan. Remove and discard the foil. Use a large chef’s knife to slice the fudge into 64 1-inch squares. Store in an airtight container.