1. Preheat oven to 300 degrees. Roast hazelnuts on a baking sheet until fragrant and lightly toasted, 10 to 12 minutes. Let cool briefly, then rub off skins with a clean kitchen towel. Coarsely chop hazelnuts.

2. In the bowl of an electric mixer fitted with the whisk attachment, beat egg whites on medium-low speed until foamy, about 4 minutes. Increase speed to medium-high and gradually add sugar. Beat until meringue is stiff and shiny, 3 to 5 minutes. Beat in vanilla and salt.

3. Scrape meringue into a large heavy-bottomed saucepan. Add chopped hazelnuts. Cook over medium heat, stirring constantly and scraping bottom of pan to make sure meringue does not burn, until mixture is light brown and pulls away from sides of pan, about 15 minutes. (Mixture will look curdled after first 5 minutes of cooking.)

4. Increase oven temperature to 325 degrees. Remove pan from heat and let cool to room temperature. Fold in chocolate.

5. Scoop mounds, about 2 tablespoons each, onto a parchment-lined baking sheet, spacing about 1 inch apart.

6. Bake until cookies are crisp on outside but soft and chewy inside, 25 to 30 minutes. Transfer sheet to a wire rack and let cool completely. Cookies can be stored in an airtight container at room temperature up to 1 week.