Preheat oven to 350℉ and place hazelnuts on a baking sheet. Roast for 10 minutes.
Transfer the roasted hazelnuts along with a pinch of salt (if using) to a food processor and process for 5-7 minutes, stopping to scrape down the sides as needed, until it becomes smooth and creamy. It may take longer depending on how powerful your food processor is. Be patient - it will get there!
If using, add your desired flavor mix-ins (such as maple syrup or vanilla) and process for another 3-5 minutes, until it becomes creamy and silky. It will likely form back into a ball when you add it, but it will become smooth and creamy again.
Once desired texture is achieved, pour into jars and enjoy! If it were me, I would eat it with a spoon straightaway.