Add one teaspoon of salt to a large pot of water over high heat and bring it to a boil.
Add the ziti to the boiling water and cook per the instructions on the package for al dente. (the pasta will cook a little more during the baking process so it’s important that the pasta isn’t over cooked)
When the pasta is at al dente remove from the pot from the stove and carefully drain the pasta.
Once drained return the pasta to the pot (off the heat).
Add the butter to the pasta and stir to combine. this will help to keep the ziti from sticking together (you can use olive oil if you prefer) and set aside until needed.
While the pasta is cooking begin cooking the sausage. Place a large skillet over medium heat.
When the pan is hot Add the chopped onion to the pan and season with salt and black pepper. Let the onions cook over medium heat for 5-7 minutes until they begin to caramelize. Stir as needed so the onions don’t burn.
Add the minced garlic to the pan and continue to cook the garlic for 1-2 minutes until the garlic is fragrant.
Add the sausage meat to the pan and increase the heat to medium-high.
Stir the meat, breaking up all the big pieces and cook until the meat is well browned. Remove the pan from the heat.
Add the ziti, ricotta mixture and sausage mixture to a large bowl.
Stir until all the ingredients are well blended.
Add three cups of tomato sauce to the mixture.
Mix well to fully combine.
Preheat the oven to 350 degrees F.
Add a layer of sauce to coat the bottom of a large baking dish.
Pour the ziti mixture into the baking dish.
Add the remaining sauce to the top of the baked ziti mixture.
Place the baking dish on the center rack of the preheated oven and bake for 30 minutes.
Carefully remove the baking dish from the oven and top with the remaining shredded mozzarella cheese, then sprinkle the finely chopped Italian parsley on top of the cheese.
Place the baked ziti back into the oven and continue to bake until the mixture is hot and bubbly.
Let the baked zit rest for 10-15 minutes before serving.