Spread the hazelnuts in a single layer onto a baking tray, and roast for 15 minutes.
Remove from the oven, and place into a food processor or high-speed blender. Blitz for a few minutes, until you have a thick and creamy nut butter. (You'll probably need to stop and scrape down the sides of the bowl - or jar - a few times.)
While the nuts are processing, break the chocolate into small pieces, and place into a heatproof bowl over a pan of hot (not boiling) water, with the coconut oil.
Once the nut butter is ready, add the melted chocolate and coconut oil, maple syrup, hazelnut milk, vanilla, and salt. Blitz for another couple of minutes, until everything is completely mixed together and smooth.
Transfer to a sterilised jar, and store at room temperature. Assuming it's around that long, this vegan Nutella will keep for around a month.