Spinach Artichoke Casserole

This is a wonderful recipe for a crowd. Who thought spinach could be so good?

2 pkgs chopped frozen spinach, thawed and well drained
1/2 medium onion, chopped
1 can artichokes (unmarinated), cut into quarters
1/2 cup parmesan cheese
1 pint sour cream
4 Tablespoons butter

Saute the onion in butter. Mix with the remaining ingredients and put into a casserole dish. Bake at 350 degrees for 30 minutes. Makes 10 servings.