In a large skillet, cook the beef, onion and garlic over medium heat until it isn’t pink anymore; drain. Stir in the spaghetti sauce and stewed tomatoes. Bring to a boil. Reduce heat and simmer uncovered for 20 minutes.
In a large pot, cook the pasta according to package directions. Drain and then rinse them with cold water.
Grab two 9″x13″ casserole dishes and set them side by side. I do both casseroles at the same time, but it’s up to you if you want to fill one, and then fill the other.
FOR ONE CASSEROLE: Spoon 1/4 of the shells into your casserole dish, spread them out. Next, top the shells with 1/4 of the meat sauce. Next spread a layer of the sour cream over the meat sauce. On top of the sour cream, place 4 slices of provolone cheese spread out. Now layer another 1/4 of the pasta, another 1/4 of the meat mixture, another layer of sour cream and top with 4 slices of Mozzarella cheese.
Cover the dish with a piece of tin foil and bake at 350 degrees for about 30-40 minutes.
At 30-40 minutes remove tin foil and allow to continue cooking for about 5-10 minutes longer or until cheese is completely melted, turning golden and bubbly. Allow to sit on counter for about 5-10 minutes. Serve hot.
Notes
While your first casserole is baking, finish preparing the 2nd casserole exactly as you did the first. Cover and pop in the freezer for a later meal. To serve the 2nd casserole, thaw the dish in the refrigerator overnight, remove from fridge and uncover about 45 minutes before cooking. Cook at 350 for 30-40 minutes.