Bake or microwave potatoes until tender. Cut in half lengthwise and scoop out almost all of the potato into a bowl.
Add milk, butter, salt and sugar to the bowl and mash. Since the mashed potatoes are the glue, we usually also throw an egg or two in there for good measure. Set aside.
Remove the casings from the spicy sausage and brown the meat in a skillet. Cook bacon, if using, in another skillet until crispy.
These can be made two ways: In a cast-iron pan or buttered/sprayed casserole dish, or in a greased cupcake pan for individual serving sizes. To assemble, place potato skins down in dish then fill with a layer of sausage, a very thin layer of mashed potatoes, a thin layer of cheese, a slice of ham, a very thin layer of mashed potatoes, a thin layer of cheese, a slice of prosciutto, a very thin layer of mashed potatoes, some bacon and top with cheese.
If using a cast-iron pan, you can throw it directly on a grill or transfer to a 400°F oven. Cook 20-30 minutes until bubbly and brown.
Top with diced scallions, sour cream and salsa if desired, and serve.