To roast the hazelnuts, spread them in a single layer on a rimmed baking sheet. Toast the hazelnuts in the oven until they start to smell wonderfully like nuts, and their skins become blistered and loose, about 10 minutes, stirring them a few times. Keep an eye on them to make sure they don't over-brown. You want them lightly golden and crisp.
To remove the brown papery skins (optional), immediately gather the warm hazelnuts up in a clean kitchen cloth* and rub them together to release the skins. You can expect some of the skins to remain stubbornly attached. In my experience, rarely do 100% of the skins come off. Note, as they cool, they also become more difficult to peel.
Let cool completely.
Notes
Oven Temperature -250℉ (120℃) is not set in stone. You could try 400℉ (200℃) for about 5-8 minutes, or 325-350℉ (160-180℃) for a little longer. Experiment, and find what you like best. Just make sure to keep your eye on them, and stir at least once. And remember to jot down how long it took, for next time.Roasting Hazelnut Flour - If you are using raw hazelnut flour for a recipe, you can roast it to enhance its flavor following the same manner. Keep an even closer eye on it though, as it toasts more quickly than whole hazelnuts.Peeling Hazeluts - In a pinch, a paper lunch sack or paper towels can be used too, but can rip after a little while of friction. To Roast Hazelnuts in the Skillet - Peeled hazelnuts are the easiest to skillet-roast. I recommend using a small stainless steel skillet. You can either dry-roast them or add just enough olive oil (or melted butter) to barely coat them with a film. Heat over medium heat, stirring often with wooden spoon. They are done when the nuts begin to have a nice aroma. You don’t want them to be brown in the middle. If you use oil, immediately place on paper towels to blot.Storing - Store away from light in an airtight container. They store well for about a month in the refrigerator, or for a couple of months in the freezer. Discard if smell rancid. Let come to room temperature for full enjoyment.