How to Make It
Using your hands, crush the tomatoes into a slow cooker and add their juices. Add the olive oil, tomato paste, basil sprig, crushed red pepper and half of the garlic. Cover and cook on high for 3 hours, until the tomato sauce is very flavorful.
Meanwhile, in a large bowl, mix the ground chuck with the remaining garlic and the bread crumbs, egg, 3 tablespoons of Parmigiano-Reggiano, 1 tablespoon of kosher salt and 1/2 teaspoon of pepper. Roll the mixture into 18 meatballs, being careful not to pack them too firmly.
Add the meatballs to the sauce. Cover and cook on high for 1 hour longer, until no trace of pink remains in the center of the meatballs. Discard the basil sprig. Add 1 tablespoon of the sliced basil to the sauce and season with salt and pepper. Spoon the meatballs into bowls, sprinkle with the remaining 1 tablespoon of sliced basil and serve, passing grated cheese at the table.