Artichoke and Spinach Casserole

2 - 10 ounce packages of spinach, cooked according to package directions. Drain well.
20 ounce can artichoke hearts, drained
1/2 pound diced mushrooms
1 cup sour cream
1/2 cup milk
3/4 cup mayonnaise
1/4 cup lemon juice
6 tablespoons butter
1 tablespoon flour
1/4 teaspoon salt
1/8 teaspoon garlic powder

In a skillet, melt 4 tablespoons of butter. Saute the diced mushrooms, set aside.  Melt the remaining 2 tablespoons of butter. Add the flour, milk, salt and garlic powder. Cook until thickened. Add spinach and mushrooms.

In a casserole dish arrange the artichokes on the bottom. Pour the mushroon mixture on top.

In the skillet, mix the sour cream, lemon juice and mayonnaise. Heat until smooth. Pour over the top of the vegetables. Bake 20 minutes at 375 degrees.