I have this tendency to just toss things together without even a hint of a recipe. This casserole is one of those things. My family really liked it though so I jotted down what passes for a recipe before I forgot what I put in it. This is a rather large recipe so you may want to cut it in half, or even thirds.
16 ounce package small shell pasta, cooked
6 boneless, skinless chicken breasts, cooked and cubed
1 cup mayonnaise
Salt and pepper to taste
8 ounces shredded sharp cheddar (2 cups)
2 cans condensed cream of celery soup (10.5oz cans)
1 can condensed cream of mushroom soup (10.5oz cans)
16 ounce package frozen pearl onions
32 ounce package frozen 'California Blend' mixed vegetables (broccoli, cauliflower, carrots)
2 cups boiling water
2 generous teaspoons chicken soup base
3 ribs celery, thinly sliced
2 tablespoons butter
In a large, heavy pot (a large Dutch oven for instance), saute celery in butter until celery is soft. Dissolve soup base in water and add to celery with the pearl onions and mixed vegetables. Cover and cook until vegetables are thawed. Add soups and cheese and heat until cheese melts. Remove from heat and add remaining ingredients.
Bake, uncovered, at 425º for 30 minutes.