Preheat the oven to 350F.
Spread the hazelnuts into a small baking tray. Roast for 10 to 14 minutes, or until golden and wafting a rich toasted scent.
Let cool slightly. Once the nuts are cool enough to be handled, transfer them to a clean kitchen towel. Grasp the edges of the towel in one hand and use the other hand to roll the nuts within the towel to release as many of the skins as possible (this creates a smoother Nutella). Don't worry if some of the skins remain! It's (almost) impossible to get them all using this method.
Discard the skins and transfer the hazelnuts to a food processor. Process for 6 to 8 minutes, stopping to scrape down the sides as needed, or until ground into a smooth nut butter.
While the nuts process, melt the chocolate in a double boiler (or in the microwave in 30-second increments) until smooth and glossy. Set aside.
Once the nut butter is smooth, spoon the melted chocolate into the food processor and add the salt. Process again for 30 seconds to 1 minute, or until incorporated and smooth, stopping to scrape down the sides as needed.
Transfer to an airtight jar and store at room temperature for up to 2 weeks.