In a large saucepan cook onion and green pepper in the 2 tablespoons of butter until tender.
Combine onion mixture in a bowl with chopped chicken and green chili peppers.
For sauce, in the same pan melt 3 tablespoons butter.
Stir in flour, coriander and salt.
Stir in chicken broth all at once.
Cook and stir till thickened and bubbly.
Remove from heat.
Stir in sour cream and 1/2 cup of the cheese.
Stir 1/2 cup of the sauce into the chicken mixture.
Fill each tortilla with about 1/4 cup of the chicken mixture.
Roll up and arrange in a 13x19x2 baking dish.
Pour remaining sauce over and sprinkle with remaining cheese.
Bake, uncovered in a 350 oven about 25 minutes or until bubbly.
Can be made ahead of time and frozen. Place a large sheet of heavy duty foil in your baking dish with enough foil over the end to fold up and over the frozen casserole. Make the casserole up until you are ready to bake it. Freeze it solid. Remove frozen casserole from your dish and encase in the excess foil for storage. This frees up the dish for other meals. When you wish to heat it, remove foil from the still frozen casserole, and place back into the dish that you froze it in initially to thaw; bake as directed.