Pre-heat the oven to 180C / 350 F.
Place the hazelnuts on a baking tray and bake in the oven for around 10 minutes (give them a shake half way through), until the skins darken.
Transfer the hazelnuts to a clean tea towel or some kitchen paper and rub them all over to remove the skins.
While the hazelnuts are roasting, place the sugar in the Thermomix bowl and mill for 10 seconds / speed 9. Set aside.
Add chocolate to the bowl. Grate for 4 seconds / speed 9 and then melt for 3 minutes / 50 degrees / speed 2. Set aside and clean the bowl.
Once the hazelnuts are ready, place them in the Thermomix bowl and blend for 1 minute / speed 9. Scrape and repeat for 30 seconds / speed 9. Repeat for 3-4 times until you are happy with the smooth consistency (note that it will always maintain a certain amount of graininess, it will not be super smooth).
Add the sugar, cocoa powder, coconut oil, melted chocolate and vanilla extract. Blend for 30 seconds / speed 4.
Scrape down the sides and blend again for 1 minute / speed 6.
Transfer to a clean jar and leave to cool. It will firm up as it cools.