Brown sausage and drain on paper towels.
Butter a 9x13 ovenproof baking pan. Spread butter evenly on 6 slices of bread and layer in pan with the buttered side facing down.
Add a layer of sausage, spreading evenly, then add a layer of cheese.
Cover the sausage and cheese layer using 6 buttered slices of bread with the buttered side facing up.
Mix together dry mustard and salt. Combine milk, eggs, mustard and salt.
Pour milk mixture over top of bread and allow to stand overnight in the refrigerator.
The following day, bake at 350°F for 1 hour.
Remove from oven and allow 20 to 30 minutes before cutting into serving sized pieces.
Can be frozen. Leftovers can be reheated in the microwave.
