Preheat oven to 350 degrees, with racks in upper and lower thirds. In a food processor, pulse hazelnuts until finely ground. In a medium heatproof bowl, combine egg whites, sugar, and pinch of salt. Set bowl over (not in) a pot with 2 inches simmering water and cook, whisking constantly, until warm to the touch, about 3 minutes. Remove bowl from heat and, using an electric mixer, beat mixture on high until thick and glossy, 3 minutes. With a rubber spatula, fold in hazelnuts.
Drop batter by heaping tablespoonfuls, 2 inches apart, onto two parchment-lined baking sheets. Bake until cracked on top, about 18 minutes, rotating sheets halfway through. Let meringues cool to room temperature.
Meringues can be stored in an airtight container, up to 3 days.