01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Boil jumbo pasta shells in salted water according to package directions until al dente. Drain and set aside.
03 - Brown ground beef in a large skillet over medium heat. Add onion and garlic; sauté until softened, about 2-3 minutes. Season with Italian herbs, salt, and pepper. Remove from heat and cool slightly.
04 - Combine ricotta cheese, egg, Parmesan, 1 cup mozzarella, and parsley in a large bowl. Fold in the cooled beef mixture until well blended.
05 - Mix marinara sauce and heavy cream in a separate bowl. Spread half the sauce mixture evenly across the bottom of the prepared baking dish.
06 - Fill each pasta shell with approximately 2 tablespoons of the beef-ricotta mixture. Arrange stuffed shells in the baking dish in a single layer.
07 - Pour remaining sauce evenly over the stuffed shells. Sprinkle with 1/2 cup mozzarella and 2 tablespoons Parmesan cheese.
08 - Cover dish with foil and bake for 25 minutes.
09 - Remove foil and continue baking uncovered for 10 minutes, or until cheese is bubbly and golden brown.
10 - Let rest for 5 minutes before serving. Garnish with additional parsley if desired.