Preheat the oven to 400°F. Lightly spray a 9 x 13-inch or 3-quart casserole dish with cooking spray, then set aside.
In a medium skillet, melt the butter over low-medium heat, then add the onions. Cook the onions until they begin to soften, about 3 to 5 minutes, then add the garlic. Cook for an additional 30 seconds.
1 tablespoon unsalted butter, 1 cup white onion, 3 garlic cloves
In a large bowl, combine the onions, garlic, chopped chicken, sour cream, salsa verde, tomatoes, green chiles, and cumin. Set aside.
5 cups cooked chicken, 2 cups sour cream, 16 ounces salsa verde, 10 ounces diced tomatoes and green chiles, 4 ounces green chiles, 2 teaspoons ground cumin
Cut the tortillas into quarters. Spread one fourth of the chicken filling into the bottom of the baking dish. Top with 1 cup of shredded cheese, then place a layer of tortillas over the cheese. It’s okay if the tortillas overlap some. Repeat this process of chicken filling, cheese, and tortillas 2 more times (total of 3 layers) making sure to use all the tortillas. Spread the last of the chicken filling on the top, then top that with the last cup of cheese.
20 corn tortillas, 4 cups sharp cheddar cheese
Bake for 20 to 25 minutes until the cheese is melted and the sides are bubbly. Cool for 10 to 15 minutes before serving.
Notes
The calories listed are an approximation based on the ingredients and a serving size of 1.5 cups of the King Ranch chicken. Actual calories will vary. Leftovers can be stored in a sealed container, in your fridge, for up to 3 days.