Pulse the hazelnuts until finely ground, about the consistency of grated parmesan.
Notes
For the most elegant and refined sweets, use peeled (roasted or blanched) hazelnuts, and process to a fine ground.
For sweets with a more rustic texture, color and taste, use hazelnuts with the skins on. If you like, leave a small portion of the nuts coarsely ground, with bigger granules here and there.
Sometimes I add a small pinch of salt to enhance the nutty flavor.
I have also used successfully a stick immersion blender attached to the processor bowl that came with it.
Storing
Stores well in an airtight container in the refrigerator for a month, or in the freezer for a couple of months. Discard is smells rancid.
Tools
Food Processoror a stick immersion blender attached to the processor bowl that comes with it