Cook the Pasta Shells: Bring a large pot of heavily salted water to a rolling boil. Add the jumbo pasta shells and cook according to the package directions until they are al dente (still firm to the bite). It’s very important not to overcook them, as they will continue to cook in the oven and can become mushy. Drain the shells carefully and rinse with cold water to stop the cooking process. You can toss them with a little olive oil to prevent them from sticking together while you prepare the filling.

Prepare the Spinach: This is the most crucial step for a non-watery filling. Place the thawed spinach in the center of a clean kitchen towel or several layers of heavy-duty paper towels. Gather the corners of the towel and twist, squeezing as hard as you can over a sink to remove every last drop of excess water. You should be left with a dense, dry ball of spinach.

Make the Three-Cheese Filling: In a large bowl, combine the 32 ounces of ricotta cheese, 1 cup of the shredded mozzarella, ½ cup of the grated Parmesan, the beaten egg, minced garlic, Italian seasoning, salt, and pepper. Add the squeezed-dry spinach and the optional fresh parsley. Mix everything together with a spatula until it is well combined.

Prepare for Assembly: Preheat your oven to 375°F (190°C). Spread about 1 to 1 ½ cups of the marinara sauce evenly over the bottom of a 9×13 inch baking dish. This will prevent the shells from sticking and create a flavorful base.

Stuff the Shells: This is the fun part! You can stuff the shells in two ways:

• The Spoon Method: Use a small spoon to fill each cooked pasta shell with a generous amount of the cheese and spinach mixture.

• The Piping Bag Method (Recommended): For a much faster, cleaner, and more efficient process, transfer the cheese filling to a large zip-top bag. Snip off one of the bottom corners to create a makeshift piping bag. Simply squeeze the filling directly into each shell.

Arrange the Shells: As you fill each shell, arrange it snugly in a single layer, open-side up, in the prepared baking dish on top of the sauce.

Top with Sauce and Cheese: Spoon the remaining marinara sauce over the top of the stuffed shells. You can cover them completely or leave some of the filling exposed for a more rustic look. Sprinkle the remaining 1 cup of mozzarella and ½ cup of Parmesan cheese evenly over the top.

Bake to Bubbly Perfection: Cover the baking dish with aluminum foil. This prevents the top from browning too quickly before the filling is heated through. Bake for 25 minutes. Then, remove the foil and continue to bake for another 15-20 minutes, or until the sauce is bubbly and the cheese is melted and turning golden brown in spots.

Rest and Garnish: Remove the dish from the oven and let it rest for at least 10-15 minutes. This is essential! It allows the filling and sauce to set, making it much easier to serve without the shells falling apart. Garnish with additional fresh parsley before serving, if desired.