In a large skillet over high heat, brown the sausages. Once nicely colored on all sides, transfer to a paper towel lined plate to remove any excess grease.
Cut the bread, cheese and sausages into bite size pieces. Layer half of the bread, cheese and sausages into your casserole dish. Repeat with the remaining bread, cheese and sausages. Pour the melted butter on top.
In a medium bowl, whisk together the eggs, milk, mustard and salt. Pour over the casserole, cover and refrigerate overnight.
Bring the casserole to room temperature and then bake in a 300˚F oven for 1 hour covered.
Enjoy while still warm with some sliced tomatoes on the side.