Heat the oven: Heat the oven to 400 F, grease a 9-by-13-inch baking dish, and bring a large pot of water with 1 teaspoon of the salt to a boil.

Brown the sausage: Warm the olive oil in a Dutch oven over medium-high heat, add the sausage, and cook until browned and crumbled, about 6 minutes.

Cook the aromatics: Add the onion and cook until softened, then stir in the garlic and cook for 30 seconds more.

Simmer the sauce: Pour in the marinara and simmer for 10 minutes so the sauce thickens slightly.

Cook the ziti: While the sauce simmers, add the ziti to the boiling water and cook it 2 minutes shy of package directions.

Reserve water and drain: Before you drain the ziti, scoop 1/2 cup of the pasta water into a mug, then drain the pasta in a colander.

Combine the filling: Stir the ricotta with 1/4 cup of the Parmesan, 1 tablespoon of the parsley, 1 teaspoon of the salt, and the black pepper in a small bowl.

Dress the pasta: Fold the ziti into the sausage sauce, adding up to 1/4 cup of the pasta water only if the mixture looks too thick to spread easily.

Layer the pasta: Spread half of the sauced ziti in the baking dish, spoon over half of the ricotta mixture in loose dollops, then add the remaining ziti, dollop over the rest of the ricotta mixture, and scatter the mozzarella and Parmesan evenly over the top.

Bake the ziti: Bake for 20 to 25 minutes until the cheese is melted and the edges are bubbling.

Rest and finish: Let the ziti rest for 10 minutes and scatter over the remaining parsley before serving.