Bring a large nonstick skillet to med. heat. Add the sausage and cook until browned. If you are adding any veggies (all except for spinach, if using spinach add in step 2, along with the meat mixture) to the casserole you will need to add them to the sausage about halfway through the cooking process to ensure they get a good saute.
Arrange the bread on the bottom of a well buttered 13x9 inch baking dish. Scatter the well drained meat mixture over the bread. Sprinkle on the cheese.
Mix the eggs, milk, dry mustard, and salt in a bowl. Pour over the bread and meat mixture. Seal the baking dish with foil and refrigerate for at least 8 hours.
When ready to bake, remove from the refrigerator leaving the foil on and set on the counter for no more then half hour to allow the pan to get to a slight room temperature.
Bake covered with foil at 350 degrees for 40 min. Uncover and bake for an additional 12-15 min. until the top is golden. Enjoy!