Creamy Chicken Noodle Soup with Rotisserie Chicken

Name: Creamy Chicken Noodle Soup with Rotisserie Chicken
Ingredients: 2 tablespoons unsalted butter; 1 tablespoon olive oil; 2 cups chopped yellow onion (from 1 large onion); 1 cup chopped carrots (from 2 medium carrots); 1 cup chopped celery (from 2 large stalks); 1 ¾ teaspoons kosher salt; 3 tablespoons all-purpose flour; 4 cups unsalted chicken stock; 2 cups whole milk; 4 ounces uncooked whole-wheat egg noodles; 3 cups coarsely chopped rotisserie chicken breast (from 2 rotisserie chickens); 1 cup frozen green peas