Brown and crumble sausage in a skillet; set aside.
In a large bowl, beat eggs; add milk, salt, and mustard. Stir in bread cubes, cheese, and sausage.
Pour into a greased 11x7-in. baking dish. If desired, cover and refrigerate for 8 hours or overnight. Remove from the refrigerator 30 minutes before baking. Or...
Bake, uncovered, at 350° for 40 minutes or until a knife inserted in the center comes out clean.