Toast whole hazelnuts on a baking pan and bake at 375°F until the skins are mostly split and the nuts are light golden brown, about 10-15 minutes. Wrap up in a clean dish towel and let sit for 10 minutes. Vigorously rub the nuts together though the towel to break the skins off (for a better method to completely remove the skins, see
How to Peel Hazelnuts). Pour the nuts into a sieve to shake off any loose skins. Set aside to cool then coarsely chop.