Preheat the oven to 400 degrees F. Oil 2 rimmed baking sheets with olive oil.
In a large bowl, combine the pork, beef, bread crumbs, pork fat, prosciutto, parsley, 1 tablespoon of the salt, oregano, fennel seeds, and chili flakes and mix with your hands just until all of the ingredients are evenly distributed. Set aside.
In a separate bowl, whisk together the ricotta, eggs, and milk just enough to break up any large curds of ricotta. Add the ricotta mixture to the ground meat mixture and mix lightly with your hands just until incorporated. The mixture should feel wet and tacky. Pinch off a small nugget of the mixture, flatten it into a disk, and cook it in a small saute pan. Taste it and adjust the seasoning of the mixture with salt, if needed. Form the mixture into balls each weighing about 2 ounces and 1-inch in diameter, and place on the prepared baking sheets. You should have about 30 meatballs.
Bake for 15 to 20 minutes, or until the meatballs are browned. Remove from the oven and lower the oven temperature to 300 degrees F.
Sprinkle the tomatoes with the remaining 2 teaspoons salt, and then pass the tomatoes and their juices through a food mill fitted with the medium plate. Alternatively, you put the entire can of tomatoes in a large bowl, don an apron, and then squeeze the tomatoes into small pieces with your hands. Pack the meatballs into 1 large roasting pan or 2 smaller roasting pans. Pour the tomato sauce over the meatballs, cover tightly with aluminum foil, and braise for 1 to 2 hours, or until the meatballs are tender and have absorbed some of the tomato sauce.
Pull the pans out of the oven and uncover. Distribute the basil leaves throughout the sauce.
For each serving, ladle meatballs with some of the sauce into a warmed bowl. Grate grana over the top, drizzle with olive oil to finish, and serve immediately.