Preheat oven to 350°F and spray a 9x13-inch (3-quart) baking pan with nonstick spray; set aside.
Bring a pot of water on the stovetop to a boil. Cook the pasta shells to al dente according to the package, about 8-9 minutes. After cooking the pasta shells, drain and place them upside down on a baking sheet to dry.
20 dry jumbo pasta shells
In a large skillet, brown the beef on medium heat until cooked through and no pink remains, about 5-7 minutes. Drain off the rendered fat.
1 pound ground chuck
Reduce heat to medium-low. In the same skillet with the beef, heat the olive oil and add the onion. Cook until translucent, about 3 minutes. Add the garlic and cook for 30 seconds more.
1 tablespoon olive oil, 1 yellow onion, 1 clove garlic
Reduce the heat to low and add the marinara sauce. Simmer uncovered for 30 minutes, stirring occasionally.
26 ounces marinara sauce
In a medium bowl, mix the egg, cottage cheese, 1 cup of mozzarella cheese, and ½ cup of Parmesan cheese together.
1 large egg, 2 cups small curd cottage cheese, 2 cups freshly shredded mozzarella cheese, ¾ cup freshly grated Parmesan cheese
Pour about three-quarters of the meat sauce into the bottom of the prepared baking dish.
Stuff the shells with 1 rounded tablespoon of cheese mixture and arrange them on top of the meat sauce, open-side up. Spoon the remaining meat sauce in-between the shells but not directly on top of the shells.
Cover with aluminum foil and bake for 30 minutes. Remove the foil and sprinkle the remaining mozzarella and Parmesan cheeses over the shells. Bake 5-7 minutes longer, or until the cheese is melted.
Garnish with fresh basil and serve!
Chopped fresh basil leaves