Granny's Mexican Chicken Casserole

I have made my Granny's Mexican Chicken Casserole for several potluck functions. Each time, people beg me for the recipe and I hesitate. Since Granny isn't here to give her permission, I feel like it's not my recipe to share. 
However, I remember Granny as a giving person- never selfish. She would want me to share!
This recipe is my Dad's favorite meal, and when I made it last night, Ben announced it was now his favorite too! It's a winner. Of course, I have modified (as I do all of my recipes) but the original is so tasty!

Granny's Mexican Chicken Casserole

Granny Cariota; serves 4

Ingredients:

4 boneless/skinless chicken breasts

1 packet taco seasoning

1 onion, chopped

1 can cream of mushroom

1 can cream of chicken

1 can Rotel OR 1/2 C milk

Tortilla chips

1 large bag cheddar cheese

1/2 stick butter (ish)

1. Boil chicken breasts in pan on stovetop until cooked thoroughly (add enough water to cover chicken). Transfer chicken to cutting board and shred.

2. Return shredded chicken to pan (with a little water) and add taco seasoning, mix.

3. Meanwhile, in a large pan- sautee 1/2-1 chopped onion in butter. Add both soups and Rotel (or milk if no Rotel used) and simmer. May add a handful of cheddar cheese if desired.

4. Transfer seasoned, shredded chicken to soup mixture in pan. Continue to simmer.

5. Line a 9x13 casserole dish with 2 layers of tortilla chips.

6. Pour soup & chicken mixture over the chips.

7. Bake at 350 for 30 minutes. Remove from oven and add remaining cheese (enough to cover the top). Return to oven for 10 minutes or until cheese is melted.

To Serve: Place casserole over a layer of tortilla chips (from the bag-for an extra crunch) and top with sour cream!