Cut the bread into 1-inch cubes and spread in the bottom of a greased 9- by 13- by 2- inch casserole dish.
Bake the covered casserole until set and slightly golden, about 50 minutes. Remove from the oven and allow the casserole to set for 15 minutes before serving.
In a medium skillet, brown the sausage over medium heat until fully cooked and no longer pink. Remove the sausage with a slotted spoon to drain the fat. Spread the cooked sausage over the bread and top with the cheese. Then stir together the, half-and-half, dry mustard, salt and eggs. Pour this mixture over the cheese. Cover the casserole with aluminum foil and refrigerate for 8 hours or overnight.