Preheat the oven to 350 degrees and add hazelnuts to a baking sheet in a single layer.
If raw, roast for a total of 12-15 minutes. If already roasted, roast for 8-10 minutes just to warm the natural oils and loosen the skins.
This will make it easier to blend into butter.
Remove from the oven and let cool slightly. Then transfer to a large kitchen towel and use your hands to roll the nuts around and remove most of the skins .
You want to get as much as possible off because it yields a creamier Nutella. But it doesn’t have to be perfect!
Leaving excess skin behind, add hazelnuts to a food processor or high-speed blender. Blend on low until a butter is formed - about 8-10 minutes total - scraping down sides as needed.
Once the hazelnut butter is creamy and smooth, add the cacao, vanilla and salt and blend well.
Taste and adjust seasonings as needed, adding more salt or vanilla if desired.