Bring a large pot of salted water to a rolling boil and cook the pasta shells until just al dente, about 12 minutes. Drain and set aside to cool slightly.
In a sauté pan, heat olive oil over medium heat and add minced garlic. Sauté until fragrant, about 30 seconds, then add fresh spinach. Cook until wilted and bright green, about 2 minutes. Remove from heat and let cool slightly.
In a mixing bowl, combine ricotta, cooled spinach mixture, shredded mozzarella, Parmesan, beaten egg, salt, and pepper. Mix until smooth and well incorporated.
Preheat your oven to 180°C (350°F). Spread a thin layer of marinara sauce at the bottom of a 9x13-inch baking dish.
Fill each cooked shell with a generous spoonful of the ricotta and spinach mixture, then place them seam side down in the baking dish, arranging them snugly.
Pour the remaining marinara sauce evenly over the stuffed shells. Sprinkle extra mozzarella and Parmesan cheese on top for a bubbly, golden crust.
Bake uncovered in the preheated oven for 25-30 minutes, until the sauce is bubbling and the cheese is golden brown. You’ll hear a gentle bubbling and see a lovely golden crust forming.
Remove from the oven and let rest for 5-10 minutes; this helps the filling set and makes serving easier. The shells should be tender, the sauce hot, and the cheese melted and slightly crispy on top.
Garnish with fresh herbs if desired, then serve hot, enjoying the creamy filling and tender pasta in every bite.
