One-Pot Chicken Tetrazzini

Heat butter in a saucepan over medium heat. Add onion and celery and cook until tender, about 5 minutes. Add broth, spaghetti, chicken meat, condensed cream of chicken soup, and sliced mushrooms. Cover and bring to a boil, about 5 minutes. Reduce heat and simmer until spaghetti is tender, about 20 minutes.