Preheat oven to 350 degrees. Cover spinach in pan of water, cook until boiling, then drain well to remove all water. Combine spinach with shredded cheese. In a separate bowl, combine other ingredients. Mix well, then add to spinach/cheese mixture.
Melt butter/margarine in casserole dish. Add mixture to dish, spread evenly and bake 45 minutes. Do not overcook, or souffle will be dry. Cut into squares to serve.