Preheat your oven to 350. Spray a baking dish with a non-stick spray.
Heat lightly salted water or some chicken broth in a medium sauce pan. When water is boiling add chicken, turn down the heat and cover with lid.Poach the chicken until it’s cooked through.( You can do this in advance and just store in the fridge until you are ready to use it. You can also use store bought rotisserie chicken) When the chicken is cool enough shred it with a fork.
Add the shredded chicken, 1 cup mozzarella and the green enchilada sauce to a large mixing bowl.Mix to combine.Taste and season with salt and pepper if you like.
Put the enchiladas together by placing about ¼ cup of the chicken mixture in the center of a tortilla, spread it out lengthwise a little bit then roll the tortilla up.Place it seam side down in the baking dish.
Melt the butter in a medium sauce pan over medium heat then whisk in the flour.Keep whisking for a minute or until all the flour is incorporated into the butter and it’s cooked through. Next add the 1½ cups of chicken broth. If you poached your chicken in broth, use that. Whisk it until smooth. Turn up the heat a bit and let the sauce thicken. When it thickens to your liking turn down the heat a bit and add in the sour cream and green chilies.Mix it well then taste.Season with salt and pepper.
Take your sauce and pour it over the enchiladas making sure they are completely covered. Sprinkle the remaining cheese over the top.
Bake for 20 to 25 minutes.
Garnish with chopped parsley or cilantro and serve with your favorite salsa. I also served with corn and peppers sauted in butter!