1/2 cup grated Parmesan cheese, plus more for topping
1/4 cup heavy cream
1/2 teaspoon salt
1/4 teaspoon black pepper
1 (24 ounce) jar marinara sauce
2 cups shredded mozzarella cheese
Instructions
Preheat your oven to 375 degrees Fahrenheit. Lightly grease a 9×13 inch baking dish.
Cook the jumbo shells according to package directions until al dente. Drain them well and rinse with cold water to stop cooking. Set aside.
Heat the olive oil in a skillet over medium heat. Add the chopped onion and cook until soft, about 5 minutes. Add the minced garlic and cook for 1 minute more until fragrant. Remove from heat.
In a large bowl, combine the squeezed dry spinach, ricotta cheese, beaten egg, 1/2 cup Parmesan cheese, heavy cream, salt, pepper, and the cooked onion and garlic mixture. Mix until the filling is smooth and creamy.
Spread about 1 cup of the marinara sauce evenly over the bottom of the prepared baking dish.
Carefully stuff each cooked shell with the spinach and ricotta mixture. Arrange the filled shells in a single layer in the baking dish.
Pour the remaining marinara sauce over the stuffed shells.
Sprinkle the shredded mozzarella cheese evenly over the top layer of sauce and shells. Sprinkle with extra Parmesan cheese.
Bake for 25 to 30 minutes, or until the sauce is bubbly and the cheese is melted and lightly golden brown.
Let the dish rest for 5 minutes before serving.
Notes
Squeeze the thawed spinach very dry; excess water makes the filling runny.
For an extra creamy sauce, stir 1/4 cup of cream cheese into the marinara sauce before pouring it over the shells.
You can assemble this dish up to 24 hours ahead; cover and refrigerate, then add 10 minutes to the covered baking time.