Preheat the oven to 225°F. Line two baking sheets with parchment paper and set aside. Add the egg whites to the bowl of a stand mixer. Whip the egg whites on high speed with a whip attachment. When the egg whites begin to stiffen and create soft peaks, add the salt and begin to slowly add the sugar. Add the sugar in several small increments.
Once the sugar is fully incorporated, continue beating the egg whites until it has dissolved completely. You can tell if the sugar is dissolved by rubbing a little meringue between two fingers – it should feel completely smooth with no grains of sugar in it. If you still feel the sugar, continue to beat the meringue. This will take about 6 to 8 minutes.
Roughly chop the toasted hazelnuts. Once the meringue is fully whipped, fold in the hazelnuts. Spoon heaped tablespoons of the meringue onto the prepared baking sheets, leaving a little space between them.
Bake the meringues for 2 hours. When done, turn the oven off. Use a ball of aluminum foil to prop the oven door open and leave the meringues in the oven for another hour. Remove and allow to cool completely.