1) Bring a large pot of lightly salted water to a boil. Add jumbo shells and cook for 8 minutes or until al dente, drain.
2) Peel the tomatoes (to make this process easy, detach the stems and then cut a very shallow X on the opposite the stem side of each tomato. Then drop them into the boiling water and leave there for 30 seconds. Remove the tomatoes and when they are cool, peel the skin off with your hands). Grate them.
3) Preheat oven to 350 degrees F (175 degrees C).
4) In a large skillet heat 2 tablespoons olive oil over medium-high heat. Saute onion for about 3 minutes. Add beef and cook it with onion over medium heat until the meat is no longer pink.
5) Stir in tomatoes and tomato paste, basil, salt and pepper. Cook for another 5 minutes. Add garlic and turn off the heat.
6) Fill the shells with the meat sauce, using a teaspoon, and arrange them in a previously greased baking dish.
7) Top the shells with Mozarella cheese.
8) Cover with foil and bake for 30 minutes. Remove the foil, sprinkle the shells with Parmesan cheese and bake for another 10 minutes, until the cheese has melted and the top is golden brown.
9) Remove from heat, let rest for 3 minutes and serve.