Mix together the salt, potatoes, onion, and butter, and press into large 11x14
glass baking dish. Bake at 425* for 1/2 hour. (If using spinach instead of potatoes, bake for only 15 minutes at 350*.) Sprinkle on the sausage, optional vegetables, and cheese. Whisk eggs, milk and/or cream, and pepper together and pour this liquid mixture over everything. Poke a fork into the bottom of the baking dish in several places to make sure it gets down in there good, and then bake at 350* for about 30 minutes. Since the baking dish is nice and hot already, it doesn't take long for this egg mixture to set.