01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or olive oil.
02 - Boil jumbo pasta shells in salted water until al dente according to package directions. Drain thoroughly and arrange on a clean surface to cool slightly.
03 - Brown ground beef in a large skillet over medium heat, breaking it apart with a spatula. Add diced onion and minced garlic; sauté for 2-3 minutes until softened. Season with Italian herbs, salt, and pepper. Remove from heat and allow to cool for 5 minutes.
04 - Combine ricotta cheese, egg, Parmesan, 1 cup mozzarella, and chopped parsley in a large bowl. Mix until fully incorporated. Gently fold in the cooled beef mixture until evenly distributed.
05 - Whisk together marinara sauce and heavy cream in a separate bowl until smooth. Spread half of the sauce mixture evenly across the bottom of the prepared baking dish.
06 - Fill each cooked shell with approximately 2 tablespoons of the beef-ricotta filling. Place filled shells open-side up in the baking dish, arranging them in a single layer.
07 - Pour the remaining sauce mixture over the stuffed shells, ensuring even coverage. Sprinkle with 1/2 cup mozzarella and 2 tablespoons Parmesan cheese.
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 the oven for an additional 10 minutes, or until cheese is bubbly and lightly golden. Let rest for 5 minutes before serving to allow filling to set.