Step 1

Arrange a rack in the middle of the oven and heat the oven to 375°F. Meanwhile, bring a large pot of salted water to a boil. Add 30 jumbo pasta shells and cook according to package directions. Drain, then briefly rinse with cold water until cool enough to handle.

Step 2

Place 1 pound ricotta cheese, 2 cups of the shredded mozzarella cheese, 1/4 cup finely chopped fresh parsley leaves, 1/4 teaspoon kosher salt, and 1/4 teaspoon ground black pepper in a large bowl and stir to combine. Taste and add more salt if needed; the overall saltiness will depend on the cheeses used.

Step 3

Spread 1 cup of the marinara sauce on the bottom of a 9x13-inch baking dish. Stuff each shell with about 1 heaping tablespoon of the mozzarella filling and place filling-side up in the dish. If some shells split during the cooking process, you may have a few fragments left over, but you should end up with about 2 dozen shells in the dish.

Step 4

Top the shells evenly with the remaining 2 cups marinara sauce. Sprinkle with the remaining 1 cup shredded mozzarella and finely grated Parmesan or Pecorino cheese. Bake uncovered until the cheese is melted and the sauce is bubbling, about 30 minutes.