Cook the jumbo shells according to package instructions. Drain well in a colander, then spread in a single layer on a rimmed baking sheet.

Heat the olive oil in large skillet over medium heat. Add the ground beef along with 1/2 teaspoon salt and 1/4 teaspoon pepper, and break it into chunks with a wooden spoon. Cook for 5 minutes or until almost cooked through, then add the onion and garlic and cook 5 minutes longer until the onion has softened. Drain excess grease as needed.

Add the marinara sauce and bring to a boil. Reduce the heat and simmer for 15 minutes to allow the flavors to meld. Remove from heat.

Grease a 9×13" baking dish and spread half of the meat sauce over the bottom of the baking dish. Set aside.

Place the ricotta cheese in a medium bowl. Add the egg and stir well to combine. Add the parmesan cheese and basil and stir until incorporated.

Fill each jumbo shell with the ricotta mixture and place the stuffed shells in the baking dish with the meat sauce. Cover the shells with the remaining meat sauce, then top with the mozzarella cheese.

Bake covered with foil for the first 15 minutes, then remove the foil and bake for 10-15 more minutes or until bubbly and golden brown. Remove from heat and allow to cool slightly. Serve topped with freshly chopped basil as desired and enjoy!