01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or olive oil.
02 - Cook the jumbo pasta shells in salted boiling water according to package directions until al dente. Drain carefully and set aside to cool slightly.
03 - In a large skillet over medium heat, cook ground beef until browned, breaking it apart with a spoon. Add onion and garlic; sauté until softened, about 2-3 minutes. Season with Italian herbs, salt, and pepper. Remove from heat and let cool for 5 minutes.
04 - In a large bowl, combine ricotta cheese, egg, Parmesan, 1 cup mozzarella, and parsley. Fold in the cooled beef mixture until well blended.
05 - In a separate bowl, mix marinara sauce and heavy cream until combined. Spoon half the sauce mixture into the bottom of the prepared baking dish, spreading evenly.
06 - Fill each pasta shell with about 2 tablespoons of the beef-ricotta mixture. Arrange the stuffed shells in a single layer in the baking dish, opening side up.
07 - Pour the remaining sauce evenly over the stuffed shells. Sprinkle with 1/2 cup mozzarella and 2 tbsp Parmesan cheese.
08 - Cover the baking dish with aluminum foil and bake for 25 minutes.
09 - Remove foil and bake uncovered for 10 minutes, or until the cheese is bubbly and golden brown.
10 - Let the stuffed shells rest for 5 minutes before serving to set. Garnish with extra parsley if desired.