01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or olive oil.
02 - Bring a large pot of salted water to boil. Cook jumbo pasta shells according to package directions until al dente. Drain carefully and set aside to cool slightly.
03 - Heat a large skillet over medium heat. Add ground beef and cook until browned, breaking apart with a spoon. Add diced onion and minced garlic; sauté until softened, 2-3 minutes. Season with Italian herbs, salt, and black pepper. Remove from heat and let cool for 5 minutes.
04 - In a large bowl, combine ricotta cheese, egg, 1/2 cup grated Parmesan, 1 cup shredded mozzarella, and chopped parsley. Mix until smooth and well incorporated.
05 - Fold the cooled beef mixture into the ricotta filling until evenly distributed throughout.
06 - In a separate bowl, whisk together marinara sauce and heavy cream until smooth and uniform.
07 - Spread half the sauce mixture evenly across the bottom of the prepared baking dish. Fill each pasta shell with approximately 2 tablespoons of the beef-ricotta filling. Arrange filled shells in a single layer in the dish.
08 - Pour remaining sauce mixture evenly over the stuffed shells. Sprinkle with 1/2 cup shredded mozzarella and 2 tablespoons grated Parmesan cheese.
09 - Cover baking dish tightly with aluminum foil. Bake for 25 minutes until heated through.
10 - Remove foil and continue baking uncovered for 10 minutes until cheese is bubbly and golden brown on top.
11 - Let stuffed shells rest for 5 minutes before serving to allow filling to set. Garnish with additional fresh parsley if desired.