Toast the hazelnuts on an oven tray in an already heated oven at 200ºC (400ºF) for 5 minutes. Take them out and turn the oven down to 130ºC (260ºF).
Put the hazelnuts in a tea-towel to rub the skins off, then chop them into small chunks.
Put the egg whites into a standing mixer and beat them at moderate speed until they become foamy. Increase the speed to maximum.
When the egg whites become white and stiff, continue beating and add the sugar tablespoon by tablespoon.
Add the vanilla essence and beat in.
The egg whites should be stiff and glossy now. Add the hazelnut chunks and mix in slowly by hand.
Use a tablespoon to put uneven blobs of the meringue mixture onto an oven tray covered with baking paper. (Use a second tablespoon to scrape them off the first one).
Bake in the oven for 1 hour then turn the heat off and leave them in there until the oven is cool.
Meringues can keep for a few weeks in an airtight container.