Mix all the ingredients together very well—you'll need your hands for the job—until you have an evenly amalgmated mixture. Form into an oval loaf.
If you want to, open up a fairly deep well in the middle of the loaf and add slices of mozzarella or another meltable cheese like scamorza. Close up the well and reform the loaf.
Now place the loaf in a baking dish.
Toss the potatoes, along with a few cherry tomatoes or wedges of regular tomatoes, with olive oil, salt and pepper in a mixing bowl until the potatoes (and tomatoes if using) are well coated. Pour them around the meatloaf. Splash on a bit of white wine over everything.
Bake in a hot oven (200 C, 400 F) for 45 minutes to an hour, tossing the potatoes and basting the loaf from time to time with the cooking juices, until the polpettone is nicely browned and the potatoes are tender and just lightly spottled on the outside. The potatoes are done when you stick a knife in them and the potato stays where it is when you lift it out.
Serve the polpettone whole, if you like, directly from the baking dish for a 'family style' meal, or slice it attractively on a serving plate, surrounded by the potatoes.