Preheat the oven to 375°F and bring a large pot of water to a boil with 1 tablespoon of salt.

Cook the ziti for 2 minutes less than the package directs, so it stays firm, then drain.

In a large bowl, stir together the ricotta, egg, parmesan and Italian seasoning until smooth.

Add the drained ziti, marinara sauce and cooked sausage (if using) to the ricotta mixture and fold together until every piece of pasta is coated.

Spread half the pasta mixture into a greased 9x13-inch baking dish (or two smaller dishes for a large crowd).

Scatter half the mozzarella over the pasta layer.

Spoon the remaining pasta mixture on top and finish with the rest of the mozzarella and a little extra parmesan.

Cover the dish tightly with foil and bake for 20 minutes.

Remove the foil and bake for another 10 to 15 minutes, until the cheese is golden in spots and bubbling at the edges.

Let the ziti rest for 10 minutes before cutting, so the layers hold together on the serving spoon instead of sliding apart.