Preheat your oven to 350°F (175°C).

In a large pot of boiling salted water, cook the pasta shells for about 8-10 minutes until al dente. Drain, rinse, and set aside.

In a skillet over medium heat, add the ground beef, onion, and garlic. Cook until the meat is browned and the onions are translucent. Drain any excess fat, then season with Italian seasoning, salt, and pepper.

In a mixing bowl, combine the cooked beef mixture with sour cream and 1 cup of shredded cheese. Mix well until combined.

Spoon the beef mixture into each pasta shell and place them in a greased baking dish. Repeat until all shells are filled.

Pour the marinara sauce evenly over the stuffed shells. Sprinkle the remaining cheese on top.

Cover with foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes until the cheese is bubbly and golden.

Let it cool for a few minutes before serving.