Add the onion and saute until soft, about 2 minutes.
Stir in the flour and chicken broth.
Add the chiles, garlic, salt to taste and cumin and simmer about 15 minutes to blend the flavors of the sauce.
Heat the oven to 350°F.
Grease a rectangular baking dish.
Put about 1/4 inch oil in a large frying pan and set over medium heat.
When hot, fry the tortillas briefly.
(Do not let them get crisp!).
Drain on paper towels.
Dip in the sauce.
Put some of the chicken in a strip on each tortilla.
Top with 2 to 3 tablespoons cheese.
Roll up enchiladas and put in prepared baking dish seam down.
Pour remaining sauce over top, then the cream. (I know this seems like a lot of cream and it does look like it might turn out runny, but after cooking it settles in and you end up with terrific, moist enchiladas and not an excess of sauce).
Sprinkle with remaining cheese and scallions.
Bake about 20 minutes (30 minutes if you are starting with cold chicken).