Make white enchilada sauce. Melt butter in a medium saucepot over medium heat. Whisk until melted and gradually add flour, stirring constantly for 1-2 minutes until flour is absorbed, thickened and a paste-like texture achieved (a roux).
Slowly pour in the chicken broth, whisk until smooth and turn the heat on low. Simmer until the mixture has thickened a bit. 7-10 minutes, if it seems too thick you have simmered it for too long or measured the ingredients incorrectly.
Add more broth or thin it out with ¼ cup water (add it gradually until sauce has become thinner). Stir in the green chilies, sour cream, ½ cup Monterey jack cheese. Set aside.
Meanwhile, preheat the oven to 350 degrees Fahrenheit.
Meanwhile, saute onion in a small nonstick pan with vegetable oil. When the onion is starting to become soft, add garlic and saute for 1 minute more. Set aside.
In a large bowl, combine rotisserie chicken, onion and garlic mixture, corn, grated cheese, spices (oregano, paprika, cumin, salt, pepper),¾ cup cheese, and 2 heaping tablespoons of white enchilada sauce. Optional Step: If not making these for kids, add another spoonful of pickled chilies into filling!
Assemble the Enchiladas. Prepare a bowl with enchilada sauce, warmed tortillas (see notes), a cutting board or a large dinner plate (for rolling up the tortillas), and the chicken mixture.
In a 9x13 baking dish pour enchilada sauce enough to cover the bottom of the dish. One by one, dip each tortilla into the white enchilada sauce, shake off the excess sauce and place it on the plate.
Fill each tortilla with about 2 heaping tablespoons of chicken mixture and roll them all up tightly. For easier rolling, I place the mixture slightly to offset the middle of each tortilla. Transfer enchiladas seam side down in the prepared baking dish.
Pour the sauce over the enchiladas, top with the remaining ½ cup of cheese (or more if desired!).
Bake for 30 minutes at 350 degrees Fahrenheit. Optional: I like to bake these for 20 minutes and then turn on the oven broiler setting and bake them for 10 minutes until cheese is slightly browned.