Spinach Casserole

2 packages frozen spinach
6 teaspoons butter
1 teaspoon flour
1/2 cup milk
1 can mushrooms
Pinch of dry mustard
1/2 teaspoon salt

Cook spinach. In saucepan, melt butter; add flour. Cook until bubbly. Blend in milk. Add seasonings, mushrooms and spinach. Pour into casserole dish.

Topping
1/2 cup sour cream
2 tablespoons lemon juice
1/2 cup mayonnaise