Heat oven to 350° F. Line a baking sheet with parchment; set aside.
Combine the brown sugar, butter, 1 teaspoon salt, and cayenne in a large pot over medium heat. Cook, stirring frequently, until melted, 2 to 3 minutes. Add the almonds, pistachios, and pecans and stir to coat.
Transfer to the prepared baking sheet and spread in a single layer. Bake, tossing once, until golden brown and glazed, 17 to 22 minutes. Stir, then let cool; break into clumps. Toss with the granulated sugar.