[The Chowhound Team split this cooking discussion from the Los Angeles board. If you're looking for a place to buy Hatch chiles in L.A. please see the original thread, here:
new mexican green chile sauce couldn't be easier to make: chop the chiles, make a thin roux with flour and oil (garlic, chopped onions, of course). add the chiles. cook briefly. you'll get some moisture out of the chiles. it won't be a thick sauce, slightly runny. warm corn tortillas in oil, warm again in chile, layer with grated cheese. top with chile. bake briefly in the oven. if you want to be completely authentic, put an over-easy egg on top of the enchiladas (i prefer before the chile, though reasonable minds disagree). if you want to be COMPLETELY authentic northern new mexican, use blue corn tortillas, but those can be tough to find around here (and don't ever bother trying to roll them ... they just fall apart).