01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or butter.
02 - Boil jumbo pasta shells in salted water until al dente according to package directions. Drain well and arrange on a clean surface to cool slightly.
03 - Brown ground beef in a large skillet over medium heat, breaking it apart as it cooks. Add diced onion and minced garlic; sauté until softened, about 2-3 minutes. Season with Italian herbs, salt, and black pepper. Remove from heat and let cool for 5 minutes.
04 - Combine ricotta cheese, egg, 1/2 cup Parmesan, 1 cup mozzarella, and chopped parsley in a large bowl. Mix until thoroughly blended. Fold in the cooled beef mixture.
05 - Whisk together marinara sauce and heavy cream in a separate bowl until smooth. Spread half the sauce mixture evenly across the bottom of the prepared baking dish.
06 - Fill each cooked pasta shell with approximately 2 tablespoons of the beef-ricotta filling. Arrange filled shells in a single layer in the baking dish, opening side facing up.
07 - Pour the remaining sauce mixture evenly over the stuffed shells. Sprinkle with 1/2 cup mozzarella cheese and 2 tablespoons Parmesan cheese.
08 - Cover baking dish tightly with aluminum foil. Bake for 25 minutes to heat through and blend flavors.
09 - Remove foil and continue baking for 10 minutes until cheese is melted, bubbly, and lightly golden. Let rest 5 minutes before serving.