One-Pot Fireman Spaghetti

Ingredients

• butter, divided
• onion, diced
• ribs celery, sliced
• ounces mushrooms, sliced
• teaspoon garlic powder, divided
• teaspoon kosher salt, divided, plus more, to taste
• teaspoon black pepper, divided, plus more, to taste
• teaspoon poultry seasoning, divided
• teaspoon Italian seasoning, divided
• chicken broth
• ounces spaghetti
• pounds chicken breasts or thighs, boneless and skinless
• sour cream
• tablespoon cornstarch
• heavy cream
• mozzarella cheese, shredded
• parmesan cheese, shredded
• cornflakes, optional, crushed