Preheat the oven to 400 degrees with a rack in the middle of the oven. Butter a 10-by-15-inch baking dish (or other large baking dish). Bring a large pot of salted water to a boil for the pasta.

In a Dutch oven, heat the olive oil over medium heat. Add the garlic and peperoncino, and cook until they’re sizzling, about 30 seconds. Add the tomatoes, fill the can with 1 cup pasta cooking water, and add that to the pot. Stir in 1½ teaspoons salt, and bring the liquid to a rapid simmer. Cook, uncovered, until the sauce is thickened, about 20 minutes. Remove the garlic cloves once the sauce is done.

While the sauce cooks, add the shells to the pasta water, and cook until they’re just al dente. Drain them, and separate them on baking sheets to avoid sticking.

To make the filling, in a large bowl, stir together the ricotta, cubed mozzarella, 1 cup of the Grana Padano or Parmigiana Reggiano, the scallions, peas, parsley, and egg. Mix the shredded mozzarella and the remaining Grana Padano or Parmigiana Reggiano in another bowl, and set both bowls aside. Stir the basil into the finished sauce.

To assemble, spread 2 cups of the sauce in the bottom of the baking dish. Divide the filling evenly among the shells, fill each shell (a small spoon works well), and arrange them in one layer in the baking dish (it’s okay to shingle them to make them flat). Top evenly with 2 cups more sauce. Sprinkle with the reserved cheese mixture. Dollop the remaining sauce evenly over the top. Tent with foil, and bake until it’s bubbly all over, 25 to 30 minutes. Remove the foil, and bake until the cheese is golden and crusty, 5 to 10 minutes more. Let the shells sit for 5 to 10 minutes before serving.