Toast the hazelnuts in a dry cast iron skillet over low-medium heat until they're lightly toasted, about 10 minutes. Transfer them into a baking sheet lined with a towel, rub the nuts to peel off as much of the outer husks as possible. Discard the husks. Allow the nuts to cool while you make the chocolate sauce.
In a small saucepan over medium-low heat, melt the chocolate with the butter, sugar and cinnamon stirring frequently, until smooth and well combined, about 7 minutes.Take the pan off the heat and continue stirring for about 30 seconds to cool slightly. Stir in the vanilla.
Transfer the nuts to a food processor fitted with the metal blade and whirl to make a thick paste, about 3 minutes. Scrape down the sides of the bowl; then, with the machine running, stream in the oil and continue to process for a full 5-7 minutes, until very smooth. With the machine still running, stream the chocolate sauce into the nut butter, using a rubber spatula to scrape out the bowl, and continue to whirl to combine well. Add the salt to the spread and blend briefly to incorporate. Adjust sugar or salt to taste.
You can eat the spread immediately slathered on a piece of bread.