1-First, preheat the oven to 375°F (190°C) and position the rack in the center. Bring a large pot of salted water to a boil and cook the ziti pasta until just barely al dente, then drain. In a large Dutch oven or stockpot, cook the sausage, onion, and garlic over medium-high heat until the sausage is browned and onions softened, about 8 minutes.

2-Next, drain excess fat from the pot. Add marinara sauce, tomato sauce, sea salt, Italian seasoning, and heavy cream; stir to combine. Mix in the cooked ziti and 1½ cups shredded mozzarella cheese thoroughly. This step ensures the pasta layers absorb the flavors of the cheese sauce.

3-Transfer the mixture to a 9×13 inch baking dish and top with fresh mozzarella slices and the remaining ½ cup shredded mozzarella. Cover with foil and bake for 20 minutes until the pasta is tender. Remove the foil, sprinkle Parmesan cheese on top, and bake uncovered for an additional 5 minutes until the cheese is melted and bubbly.