Add the hazelnuts to an oven tray and bake at 160C/320F. Bake for 15-20 minutes, checking them after 10ish minutes and every so often to make sure they haven't burned.
Take the tray out of the oven and with a towel or oven glove, rub the nuts together so that they lose their shells. Not all of the nut's shells will fall off and that's okay. Just try to remove as much shell as you can!
Add the coconut oil to the food processor and process for a good 8-10 minutes. Scrape the sides from time to time. The longer you process it (and the stronger your food processor) the smoother your nutella will be. I like mine really smooth and runny so I processed it for about 10 minutes.
Add the cocoa powder and the erythritol to the food processor and process for an additional 2 minutes.It's now done and ready to serve! Store in the fridge in a jar or tupperware. It should keep for 3-4 weeks.