Preheat the oven to 350 degrees F. Spread the hazelnuts on a baking sheet in a single layer. Roast for 12 minutes, rotating the pan halfway through.
Remove the hazelnuts from the oven and let cool for a couple of minutes.
Add the still warm hazelnuts to your food processor. Process them on high until the nuts turn into loose, fairly liquid butter, about 10 minutes, stopping to scrape the sides and bottom of the food processor bowl a few times during this process.
Add the remaining ingredients to the food processor. Process them on low for a few seconds, then process on high until very smooth, about 3 more minutes, scraping the sides and bottom twice.
Transfer the spread to an airtight container. It should keep on the counter for about a week.
Video
Notes
You do need patience because it takes a while for the toasted hazelnuts to turn into smooth, loose butter. I saw several recipes that said five minutes. But in my KitchenAid food processor, on high speed, it takes a full ten minutes.Getting smooth, loose hazelnut butter - as shown in the video below - is the key to this recipe's success and to preventing a grainy texture.