Bring a large pot of salted water to a boil, then cook the pasta shells for 8-10 minutes until just al dente. Drain and lay flat on a towel to prevent sticking.
While the pasta cooks, combine ricotta, chopped spinach, grated Parmesan, minced garlic, chopped basil, salt, and pepper in a mixing bowl. Mix until smooth and well blended, with the spinach evenly distributed.
Spread a thin layer of marinara sauce in the bottom of a 9x13 inch baking dish. This helps prevent the shells from sticking and adds flavor.
Using a spoon or piping bag, carefully stuff each shell with the ricotta mixture, filling it generously but neatly. Place the filled shells seam-side down into the prepared baking dish.
Once all shells are filled and arranged, pour the remaining marinara sauce evenly over the top, ensuring each shell is covered.
Sprinkle shredded mozzarella evenly over the sauce-topped shells. Cover the dish loosely with aluminum foil.
Bake in a preheated oven at 180°C (350°F) for 25-30 minutes, until the cheese is bubbly and golden around the edges. Remove the foil in the last 5 minutes if you'd like a more browned top.
Take the dish out of the oven and let it rest for 5 minutes. This helps the filling set, making it easier to serve neat slices.
Garnish with additional chopped basil if desired, then serve warm with extra sauce on the side. Enjoy the creamy, cheesy bites with a hint of fresh herbs in every forkful.
