Preheat oven to 350°F. Line rimmed baking sheet with foil. Spray foil with nonstick spray. Whisk egg white in medium bowl until foamy. Add sugar; whisk until frothy. Whisk in rosemary, fleur de sel, and cayenne. Add nuts; stir.
Transfer to greased baking sheet, spreading nuts in single layer. Bake until golden, stirring every 10 minutes, about 20 minutes (Check every 5 minutes after 10 min). Cool completely on sheet.