Spread the hazelnuts in a single layer on a baking sheet and toast them in the oven for about 12 minutes, until they’ve browned a little and the skins are blistered a little.
Wrap them in a kitchen towel and rub vigorously to remove as much loose skin as possible. (Some skin will cling to the nuts when you’re done. It’s okay—not to mention inevitable.) Let cool completely.
Melt the chocolate in a saucepan over gently simmering water or in the microwave. Stir until smooth. Let cool completely.
In a food processor, grind the hazelnuts until they form a paste. Add the oil, sugar, cocoa powder, vanilla, and salt and continue processing until the mixture is as smooth as possible-or as smooth as you like.
Add the melted chocolate, blend well, and then strain the mixture to remove any chunks of hazelnut that remain. The resulting Homemade Hazelnut Spread will be thin and somewhat runny, it will thicken as it cools.
Scrape your Homemade Hazelnut Spread into a jar or other resealable container and let it cool to room temperature. Cover the container after "testing" a couple spoonfuls.
*The Homemade Hazelnut Spread will be good for up to 2 weeks.