Step 1Heat the oven to 400 degrees. Coat 2 rimmed baking sheets with olive oil. In a large bowl, combine the pork, beef, bread, pork fat, prosciutto, parsley, 2 teaspoons salt, oregano, fennel seeds and chile flakes and mix with your hands just until the ingredients are evenly distributed. Set aside.
Step 2In 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 piece, flatten it into a disk, and cook it in a small saute pan. Taste and adjust the mixture's seasoning with salt, if needed.
Step 3Form the mixture into 1 1/2 -inch balls, each weighing about 2 ounces, and place on the prepared baking sheets. You should have about 30 meatballs.
Step 4Bake, rotating the sheets once from front to back, for 20 to 25 minutes, or until the meatballs are lightly browned. Remove from the oven and reduce the temperature to 300 degrees.
Step 5Sprinkle the tomatoes with the remaining salt, and then pass the tomatoes and their juices through a food mill fitted with the medium plate. Alternatively, put the entire can of tomatoes and salt in a large bowl, don an apron and squeeze the tomatoes into small pieces with your hands.
Step 6Pack 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 1 1/2 hours, or until the meatballs are tender and have absorbed some of the tomato sauce.
Step 7Remove the pans from the oven and uncover. Distribute the basil leaves throughout the sauce.
Step 8For each serving, ladle the meatballs with some of the sauce into a warmed bowl. Grate the grana over the top, drizzle with olive oil to finish and serve immediately.