Meanwhile, in 6-quart Dutch oven, melt butter over medium-high heat. Cook sausage in butter 8 to 10 minutes, stirring frequently, until no longer pink. With slotted spoon, transfer sausage to large bowl; set aside. Add onion, bell pepper, celery and serrano chiles to Dutch oven. Cook 4 to 6 minutes, stirring occasionally, until tender and lightly browned on edges.