Preheat oven to 375 degrees F. In a 15x10x1-inch baking pan combine almonds, walnuts, and pumpkin seeds. Bake about 12 minutes or until toasted, stirring once.
In a small bowl combine rosemary, brown sugar, salt, and cayenne pepper. Stir in butter. Drizzle butter mixture over nuts, tossing gently to coat. Serve warm or cooled to room temperature. Store in an airtight container for up to 3 days.