Make authentic chicken enchiladas by preparing an enchilada sauce, rolling tortillas with chicken and baking the rolled tortillas in a dish with the sauce. After baking the rolled tortillas, top them with sour cream and cheese.
Make the enchilada sauce by putting 9 husked tomatillos, 1/2 medium white onion, 1 serrano chile, 1 yellow chile and 3/4 cup of water in a medium heavy saucepan. Bring the mixture to boil over medium-high heat. Cover the pan, and boil it for about 10 minutes or until the tomatillos are cooked and olive-green. Transfer the tomatillos, onion and chiles to a blender, and blend until smooth along with 2 cloves of raw garlic and 1/2 cup of loosely-packed cilantro leaves. Season to taste with salt and freshly ground black pepper.
Heat 1/4 cup of vegetable oil in a skillet, and fry 6 6-inch corn tortillas in the pan over medium-high heat. Fry until golden but still flexible. Transfer the tortillas to paper towels to absorb excess oil.
Spread 1/3 cup of the enchilada sauce in a 9- by 13-inch glass baking dish. Divide 1 1/2 cups of shredded chicken breast among the 6 corn tortillas, and roll them into little cigars, placing each in the baking dish in a single layer, seam-side down. Pour the rest of the sauce over the enchiladas, and top them evenly with 1/2 cup of sour cream and 1 cup of shredded Monterey Jack cheese. Bake for about 30 minutes at 350 degrees Fahrenheit until the cheese melts and begins to brown. Serve immediately.