Preheat the oven to 180°C. Place raw hazelnut on the baking sheet and roast for 10-12 minutes until the skin is dark, but the hazelnuts are golden brown. Watch every few minutes because they can get easily too brown. You can also mix them on the sheet a few times, so they roast evenly.
Remove the hazelnuts from the oven and let cool slightly.
After hazelnuts cool slightly, transfer them to a kitchen towel and gently rub them all together until most of the skin comes off. Pick the hazelnuts with your fingers and place them back on the baking sheet. Let cool completely.
Fill a ¾ of the pot with water and bring it to boil. Cut dark chocolate bar into little pieces and put it into a medium-sized glass bowl. Place the bowl on the pot, turn off the heat and let the chocolate melt completely. Set aside.
Place roasted hazelnut into a high-speed blender or food processor and blend – blend on low speed until the hazelnuts are all evenly mixed. Scrape down the sides, to make sure everything blends evenly. Then blend on high speed until it forms into a creamy butter. It might take from 4-10 minutes depending on your blender/food processor.
Add the melted chocolate bar, melted flavor-free coconut oil, a pinch of sea salt, vanilla extract, and coconut sugar, and blend on a lower speed until combine. Lastly, add maple syrup and unsweetened cocoa powder and blend again until everything combines *.
Transfer the butter into a glass jar and let cool completely and thicken.
Cover with lid and store at room temperature for 3-4 weeks.