Butter a 2 1/2- to 3-quart baking dish. Heat oven to 350°.
Spread bread with the butter; cut into cubes and arrange in the bottom of the prepared baking pan.
In a large skillet, crumble the sausage and brown, stirring, until no longer pink. Drain well and sprinkle over the bread in the baking pan.
In a bowl, whisk the eggs with the milk until well blended. Whisk in the mustard, salt, and pepper. Stir in the cheese. Pour over the sausage layer.
Bake for 45 to 50 minutes, until browned and set.
Calories per serving: 445