01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or a thin layer of oil.
02 - Bring a large pot of salted water to a boil. Cook jumbo pasta shells according to package directions until al dente, typically 9-11 minutes. Drain thoroughly and arrange on a clean surface to prevent sticking.
03 - Heat a large skillet over medium heat. Add ground beef and cook, breaking apart with a wooden spoon, until browned completely, about 6-8 minutes. Add diced onion and minced garlic; sauté until softened and fragrant, approximately 2-3 minutes. Season with Italian herbs, salt, and pepper. Remove from heat and allow to cool for 5 minutes.
04 - In a large mixing bowl, combine ricotta cheese, egg, 1/2 cup Parmesan cheese, 1 cup mozzarella cheese, and chopped parsley. Mix until smooth and fully incorporated. Gently fold in the cooled beef mixture until evenly distributed.
05 - In a separate bowl, whisk together marinara sauce and heavy cream until smooth and uniform in color.
06 - Spread half the creamy sauce mixture evenly across the bottom of the prepared baking dish. Fill each cooled pasta shell with approximately 2 tablespoons of the beef-ricotta filling, using a spoon or small scoop. Arrange filled shells in a single layer, opening side facing up, in the baking dish.
07 - Pour the remaining sauce mixture evenly over the stuffed shells, ensuring each shell receives some sauce. Sprinkle with 1/2 cup mozzarella cheese and 2 tablespoons Parmesan cheese in an even layer.
08 - Cover the baking dish tightly with aluminum foil. Bake for 25 minutes to heat through and meld flavors.
09 - Remove foil and return to oven. Bake uncovered for 10 additional minutes until cheese is bubbly and lightly golden on top.
10 - Remove from oven and let rest for 5 minutes before serving to allow filling to set. Garnish with additional fresh parsley if desired. Serve warm.