Cook and drain ground beef. Stir in mushrooms.
Cook spinach according to package directions, press out water well.
Combine sour cream, cheddar cheese, parmesan cheese, milk and dry soup mix. Stir into meat mixture along with spinach.
Pour into a 9x13 pan and bake covered at 350º for 20 minutes
Meanwhile, combine croutons with butter and sprinkle on top of casserole and bake for 10 more minutes
