Creamy Chicken Noodle Soup

1 Tbsp. butter
1 large onion, finely chopped
3 C. chopped cooked chicken
3 (14 oz.) cans chicken broth
2 cans cream of celery soup
8 oz. spaghetti, broken into 2 in. pieces
2-3 celery ribs (more if desired), finely chopped
6 carrots, finely chopped
1 tsp. poultry seasoning
1 tsp. pepper
1 tsp. grated lemon rind
2 C. milk
2 C. shredded sharp Cheddar cheese

Melt butter in Dutch oven over medium heat. Add onion and saute until tender. Stir in chicken and next 8 ingredients. Bring to a boil. Reduce heat and simmer 45 min. Stir in milk; return to simmer. Remove from heat; let stand 10 min. Sprinkle each serving with cheese.