Preheat the oven to 350 degrees F (175 degrees C).
Heat each tortilla on the stove until soft and lightly puffed, about 1 minute, then tear each tortilla in half.
Pour enough enchilada sauce into the bottom of a 9x13 baking dish to coat the bottom.
Arrange 12 tortilla halves in a single layer on top of the sauce.
Layer 1/2 the chicken, 1/3 of the cheese, 1/2 of the sour cream, and 1/3 of the remaining enchilada sauce.
Repeat the layers – 12 tortillas, the remaining chicken, 1/3 more cheese, the remaining sour cream, and 1/3 more enchilada sauce.
Layer the last 12 halves of tortillas, then the remaining enchilada sauce. Sprinkle with remaining cheese.
Cover and bake in the preheated oven for 20-25 minutes, or until the cheese is melted and everything is heated through.
Cool for a few minutes, then serve warm.