To begin, roast the hazelnuts in the oven at 165ºC (fan assisted) for 15 minutes. Leave them to cool till warm-to-the-touch.
Remove the skin from the hazelnuts. To remove the skins you can either simply scrunch them in your hands or bunch them up within a clean towel and rub between your hands. The skins will fall off the roasted nuts fairly easily, this way as the friction of the nuts rubbing together will cause the skins to loosen.
Blend them in a high-speed processor/blender. It’s best to do so at intervals so the nuts (and machine) don’t overheat. The longer you blend the runnier the nut butter consistency will be. For a smooth runny hazelnut butter, blend for about 15 minutes with breaks every 2-3 minutes.
Once the hazelnut butter is ready, simply transfer it to an airtight glass container and keep this in the fridge for 2-3 months or at room temperature for around a month.