Preheat your oven to 375°F and lightly grease a 9x13-inch baking dish.
Bring a large pot of salted water to a boil over high heat. Add the jumbo shells and cook for 8-10 minutes, stirring occasionally, until they are slightly al dente. Drain the cooked shells and spread them out in a single layer on a baking sheet to cool.
In a medium bowl, mix together the ricotta cheese, mozzarella cheese, Parmesan cheese, egg, parsley leaves, basil leaves, salt and pepper until everything is combined.
Spoon 1/3 cup of the cheese mixture into each of the cooled jumbo shells. Place filled shells in the prepared baking dish.
Pour marinara sauce over the stuffed shells and sprinkle with additional Parmesan cheese, if desired.
Bake for 25-30 minutes or until heated through and the cheese is melted and bubbly.
Let cool for 5 minutes before serving.