Trim crust off bread, butter both sides, place in the bottom of a 13 x 2" pan. Brown Sausage, drain. Layer Sausage on bread, add cheese then onions. Whip eggs with s & p and 1 1/4 cup of the milk. Pour over, cover with foil and refrigerate over night. Next morning add 1/4 cup milk to soup and mushrooms and pour over. Bake 1 1/2 hour @ 300? uncovered.