The easiest way — Toast hazelnuts in a 375 degree oven for about 10 minutes. Transfer to a tea towel and use the towel to rub the skins off (it will discolor the towel). Unfortunately, it’s hard to remove all of the skins with this method.
The best way — Bring a large pot filled halfway with water to boil. Add 2 tablespoons of baking soda. Add hazelnuts and boil for 2-3 minutes until skins are loose (watch pot to make sure it doesn’t boil over). Rinse until cold water and rub skins off with your fingers. Blot dry with paper towels, then toast in a 375 degree oven for 10 minutes. While this method removes all of the skins, it is more time consuming.