4 slices white sandwich bread
1 med. onion, chopped
1 c. sliced fresh mushrooms
2 tbsp. butter, melted
1 c. cooked ham, chopped
1 c. (4 oz.) Swiss cheese, shredded
1 c. (4 oz.) Cheddar cheese, shredded
1 tbsp. all-purpose flour
1 1/4 c. milk
4 lg. eggs, beaten
1 tbsp. prepared mustard
1/2 tsp. garlic salt

Place bread slices in bottom of a lightly greased 8 inch square baking dish; set aside. Saute onion and mushrooms in butter until tender; spoon evenly over bread. Top with ham. Combine cheeses and flour; sprinkle over ham. Combine milk and next 3 ingredients; pour over cheese. Cover and chill 8 hours. Remove from refrigerator and let stand at room temperature for 30 minutes. Bake at 375 degrees for 35 minutes or until set. Let stand 10 minutes before serving. Yield 4 to 6 servings.