Preheat broiler to high

Line a baking sheet with aluminum foil and arrange the poblanos, serrano, and tomatillos on the baking sheet

Place the sheet within 6 inches of the broiler and broil until browned, flipping halfway between (tomatillos will require less time, about 7 minutes and peppers about 15 minutes

When everything is charred and blistered, transfer to a gallon-sized plastic bag, and seal until cooled allowing everything to steam (this makes it easier to skin the peppers)

When cool enough to handle, peel skins from tomatillos and chilis and seed poblanos. Seed serranos to taste (they are very hot, so seed accordingly)

Place roasted chilis, tomatillos, garlic, cumin, sour cream, and cilantro into blender and blend until smooth

Heat tortillas briefly in the microwave to soften (about 15 seconds).

Mix 1/2 cup of enchilada sauce with the chicken and combine well.

Spoon the chicken mixture over each tortilla and then roll each one up.

Cover the bottom of a 9 x 13 baking dish with a thin layer of enchilada sauce and then top with shredded cheese.

Reserve the remaining enchilada sauce for serving.

Bake the enchiladas for 25 minutes, until cheese melts.