Chicken Enchilada Casserole

2 cups chopped cooked chicken
2 cans cream of chicken soup
1 (4 oz) can green chiles
1/2 onion, chopped
1 lb cheddar or jack cheese, grated
1 pt. sour cream
3 Tbsp butter or margarine
12 flour tortillas

Heat oven to 350. Grease 9X13 pan. In medium bowl, combine sour cream, soup, and chiles. Mix well. Spoon large spoonful of mixture down each center of tortilla. Add chicken, onions, and cheese. Roll up; place in greased pan. Spoon any remaining sour cream mixture over tortilla. Cover with foil. Bake at 350 for 25-30 minutes. Sprinkle with reserved cheese. Return to oven and bake 5 more minutes.