Preheat oven to 180 degrees celsius (fan forced).
Line a large flat baking tray with baking paper. Place the hazelnuts on top and roast for 10 times, turning partway through.
Remove from the oven and transfer to a kitchen tea towel to cool. Once cooled, rub the hazelnuts until the skin comes off.
Place the hazelnuts (skins removed) into the Thermomix bowl. Mix for 30 seconds, Speed 8. Scrape down the sides of the bowl and repeat 4 times until a paste has formed.
Add the icing sugar, cocoa powder, coconut oil, vanilla extract, salt and melted chocolate to the bowl.
Mix for 30 seconds, Speed 5. Scrape down the sides of the bowl and blend for 2 minutes, Speed 6 (scraping the bowl after 1 minute).
Transfer to a sterilised jar or container and store in the refrigerator for up to 1 month.