Preheat oven to 375°F and move a rack to the top third of the oven. Bring a large pot of salted water to a boil and cook the ziti for 2-3 minutes less than the package directs. Drain and set aside.

In a large pot over medium-high heat, cook the sausage and onion, breaking up the sausage with a spoon, until browned, about 7-10 minutes.

Add the garlic, Italian seasoning, and red pepper flakes; cook for 1 minute until fragrant.

Stir in the crushed tomatoes, heavy cream, salt, pepper, and sugar. Bring to a simmer and cook for 5 minutes, stirring occasionally.

Add the drained pasta to the pot with the sauce and toss to coat evenly.

Spread half of the pasta mixture into a 9x13-inch casserole dish to form an even bottom layer.

Drop spoonfuls of ricotta over the pasta layer (no need to spread evenly—just dollop it around).

Top with the remaining pasta mixture, spreading it into an even layer (do not stir).

Sprinkle the parmesan and mozzarella evenly over the top.

Bake uncovered for 20 minutes, until hot and bubbly. Then switch the oven to broil and watch closely until the cheese is golden brown, about 1-2 minutes.

Let the baked ziti rest for 5 minutes before serving. Garnish with fresh parsley or basil if desired.