For a chocolate-hazelnut version of these meringue cookies, sift in 2 tablespoons cocoa powder when adding the nuts.
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 2 parchment-lined baking sheets. Bake until cracked on top, about 18 minutes, rotating sheets halfway through. Let meringues cool to room temperature.