Easy Spinach Casserole

4 or 5 (10 ounce) package frozen chopped spinach
1 envelope dry onion soup mix
1/4 cup margarine
1 cup sour cream
1/2 cup grated Parmesan cheese

Cook spinach according to package directions. Drain well. Add remaining ingredients. Mix well. Pour into buttered casserole dish. Sprinkle more Parmesan cheese on top. Bake at 350 degrees F for 25 minutes or until heated through.