Stuffed Shells

I haven't made these in a long time, in fact, I forgot I have made them in the past.  I like this recipe because it is prepared in 3 basic steps and can be done at once or in stages.  Mine are ready for the oven and took all of 40 minutes to get prepared.  I cooked and filled 24 shells, 12 for tonight and 12 to freeze for a few weeks from now.
For the pasta shells, boil a large pot of water over high heat.  Once it boils, add 1 tsp Salt and cook 24 Large Pasta Shells for about 12-15 minutes.  They need to be under done since they are being baked in the oven.
While water is boiling, slice 1/2 Large Onion very thinly and sautee in 1 Tbl Olive Oil for about 3  minutes until fragrant.  Add 1 lb Ground Beef and cook until just about done.  Add 4 Cups Marinara to the meat and onion.  I make my own marinara and the recipe is on this site or you can easily use a jar of your favorite.  Season the sauce with S&P to taste, Parsley, Oregano and Basil.  Let cook over low heat for for about 15 minutes.  While sauce is cooking make filling.
To a bowl add 15 oz Ricotta Cheese, 2 Cups Shredded Mozzarella, 1 Cup Parmesan, 2 Egg Yolks, 2 Pressed Garlic Cloves, S&P to taste, and 1 tsp Fresh Chopped Parsley.  If you want to add spinach to the filling I would chiffonade about 1 Cup of Clean Fresh Spinach and stir into filling.
Preheat Oven to 350F.  Drain pasta and rinse under cold water to stop the cooking process.  Butter casserole dish and add 2 cups of sauce.  Fill shells with filling and bury them in the sauce without overlapping.  Top with additional sauce as desired.   Cover dish tightly with foil and bake for 25  minutes.  Remove foil and bake for an additional 10-15 minutes until bubbly.  Let rest for 5 minutes before serving.  In the meantime, warm bread in the oven.  Serve additional sauce on the side.  Great with a simple salad.