In a large skillet or saucepan, cook onion and green pepper in 2 tablespoons butter until tender. Combine in a large bowl with the chopped green chili peppers; set aside. In the same skillet, melt the remaining butter. Blend in flour, coriander and salt. Stir in chicken broth all at once. Cook and stir until thick and bubbly. Remove from heat; stir in sour cream and 1/2 cup cheese. Stir 1/2 cup of sauce into the chicken. Dip each tortilla into the remaining hot sauce to soften. Fill each with about 1/4 cup of the chicken mixture. Roll up; arrange in a 13 x 9 x 2-inch baking dish. Pour remaining sauce over and sprinkle with the remaining cheese. Bake, uncovered, in a 350° oven about 25 minutes.