Bring a large pot of well-salted water to a full rolling boil. Cook the jumbo shells for 9 minutes (2 minutes less than package directions), drain, and spread on an oiled baking sheet to cool.

Heat a large skillet over medium-high heat. Cook the ground beef, breaking it up, for 6 to 8 minutes until no pink remains and the edges are browned. Add the garlic in the last 2 minutes. Drain fat and spread the beef on a plate to cool for 10 minutes. Confirm internal temperature has reached 75°C (165°F).

In a large bowl, combine the cooled beef, ricotta, ¾ cup mozzarella, parmesan, eggs, oregano, basil, salt, and pepper. Stir until evenly combined. Fold in the parsley.

Preheat the oven to 190°C (375°F). Spread 350ml of marinara evenly across the bottom of a 9x13 inch baking dish. Stir 125ml water or broth into the remaining sauce.

Fill each shell with about 2 heaped tablespoons of filling. Arrange open-side up in the dish, packed snugly in a single layer.

Pour remaining sauce evenly over the shells. Scatter the remaining ¾ cup mozzarella on top. Cover tightly with aluminum foil.

Bake covered for 30 minutes. Remove the foil and bake for 10 to 12 more minutes until the cheese is golden in spots and the sauce is actively bubbling at the edges. Rest for 5 minutes before serving.