Preheat the oven or grill to 400 degrees F. Line 2 rimmed baking sheets with parchment paper, or coat them with olive oil.
In a large bowl, combine the pork, beef, bread, parsley, 2 Tbsp. of salt, oregano, fennel, and chile flakes. Mix with your hands just until all of the ingredients are evenly distributed. Set aside.
In a separate (very large) 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. (It will be looser and tackier than you’d expect a meatball to be.) Pinch off a small piece 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 1 1/2 -inch balls each weighing about 2 ounces—or make humongous ones like I like to make just because—and place on the prepared baking sheets a few inches apart. You will have anywhere between 40 and 90 meatballs, depending on how insane you are.
Place two baking sheets in the oven or on the grill and bake, rotating the sheets once from front to back, for 15 to 25 minutes, or until the meatballs are browned and barely cooked through. (You can cut one open to check!) Remove from the oven. Bake any other batches of meatballs if necessary, then lower the oven temp to 300 degrees F.
Place the diced and crushed tomatoes in a bowl and add the remaining tablespoon of salt, along with a few tablespoons of olive oil. Stir.
Pack the meatballs into 1 large roasting pan or 2 smaller roasting pans. (It’s okay if they’re layered in there.) 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.
Pull the pans out of the oven or off of the grill and uncover. Distribute the basil leaves throughout the sauce.
For each serving, ladle meatballs with some of the sauce into a warmed bowl. Grate the Parmigiano-Reggiano over the top, drizzle with olive oil to finish, and serve immediately.
Reminder: If you’d like to save some of the meatballs for another time, you can bake them off, allow them to cool, and then freeze them in an airtight container. When ready to use, allow them to come to room temperature for an hour, then add the tomato sauce and braise them.