Heat 8-9 cups of water in a big pot, and bring to a boil, then cover and reduce heat to medium. Let simmer until chicken is cooked through, 10 minutes. Remove from pan and let rest 10 minutes. (Reserve 1/2 cup of broth.)
In a separate pot bring bring approximately four cups of water to a high heat NOT BOILING. Add spinach. It will cook down quickly. Drain and place to the side.
In a saucepan, on medium heat, sauté onions and garlic in the 1 tbsp butter. Place to the side.
In a large mixing bowl combine soup, cooked spinach, reserved chicken broth, onions, salt, garlic, milk, green chilies, sour cream, and shredded or chopped chicken. Mix together with a spoon until combined well (Reserve any remaining sauce for the top of the enchiladas.)
Coat 2 (13 by 9-inch) baking dishes with cooking spray or olive oil.
Place tortilla shell on a flat surface. Add a heaping spoonful of chicken mixture inside each tortilla then top with cheese, roll and place in a non-stick baking dish. After all enchiladas are placed in the dish, pour the rest of the chicken mixture across the top.
Cover with aluminum foil and place in a 350 degree oven for 25 mins.
At the 25 min mark, take off aluminum foil and top with additional cheese. Pop back into the oven uncovered long enough to melt the cheese, around 5 minutes.
Garnish with cilantro, scallions, sour cream and chopped tomatoes if desired before serving. This dish also goes great with Spanish Rice.
TO FREEZE: Cover enchiladas tightly with plastic wrap, then aluminum foil. Freeze up to 3 months. To bake, remove plastic wrap, cover and bake for 30 minutes. Uncover; continue to bake for an additional 5-10 minutes, or until completely cooked through.
The longer and slower the chicken breast cook at a low temperature the end result will be more of a shredded chicken. This makes for easier enchilada building.
Don’t add too much of the chicken mixture to the tortilla. Makes rolling harder.
These are great to make ahead of time. You can freeze then let set at room temperature before popping into the oven.