Preheat oven to 350 degrees. Grease a 9x13 inch baking dish.
Melt butter. Add chopped onion. Cook 3 to 4 minutes until soft. Add flour, cook an additional 3 to 4 minutes to remove flour taste. Add chicken broth. Cook until slightly thickened about 5 minutes.
Stir in sour cream, salsa, and rotel. Add remaining ingredients. Stir in cheese.
Put mixture into baking dish. Cover. Bake 20 minutes. Uncover and bake an additional 15 minutes, broiling a final minute if desired for browning.