Preheat oven to 350ºF. Toss the hazelnuts on a sheet pan and roast for 12-15 minutes. Remove from the oven and let cool slightly. Place roasted hazelnuts on one half of a clean kitchen towel and cover with the other half. Rub them together to help some of the skins fall off (don't go crazy—some skins are okay, but removing what you can will give you a creamier truffle!)
In a food processor, add the hazelnuts (leaving behind as many skins as possible) and buzz for 2 minutes until hazelnut butter forms.
Add in the cacao powder and salt. Pulse for 30 seconds to combine, then add the maple syrup. Buzz for another minute until the mixture tightens up into a ball.
Using a small scoop or a spoon, make balls bout 1-inch in size, pressing the 'dough' together as you roll it into a smooth ball. Sprinkle with sea salt or roll in extra chopped hazelnuts.