Roast the hazelnuts in a fan oven for 15 minutes at 150°C.
Bring the water and caster sugar to a boil at 110°C.
Add the hot nuts.
Stir sandy and then caramelize the mixture.
Sprinkle with the fleur de sel.
Then cool to room temperature on a baking sheet.
When cold, blend in a Robot Coupe® until an old-fashioned praliné (large grains).