Remove crusts from bread slices and spread butter on both sides.

In a 13" x 9" baking dish, place 6 slices of bread in 2 rows and top with half of the cheese.

Place remaining 6 slices of bread on top and sprinkle with remaining cheese.

In a large bowl, beat together eggs and milk.

Pour egg mixture evenly over top of casserole.

Sprinkle with salt.

Cover and refrigerate overnight.

Preheat oven to 300°.

Bake soufflé covered for 1 hour and 20 minutes. Do not open oven door during baking.