Prepare Pasta: Bring a large pot of salted water to a rolling boil. Add the ziti noodles and cook them just until they are very al dente—about 6 to 7 minutes—since they will continue softening in the oven. Drain thoroughly and return the pasta to the pot. Set aside for later.
Cook Sausage: Place a large nonstick skillet over medium-high heat. Crumble the sausage into the pan and cook, stirring frequently, until browned and fully cooked through, about 5 to 6 minutes. Use a slotted spoon to remove the sausage onto a plate, leaving behind any rendered fat except about 1 tablespoon. If there isn’t enough fat, add 1 tablespoon olive oil.
Sauté Garlic and Simmer Sauce: Reduce the heat to low and add the minced garlic to the skillet. Stir constantly for about 1 minute until fragrant but not browned. Pour in the crushed tomatoes and stir in salt, sugar, and red pepper flakes. Let this simmer gently, uncovered, for 10 minutes to meld flavors.
Finish Sauce: Stir in the heavy cream, half of the Pecorino Romano cheese (⅓ cup), the cooked sausage, and chopped basil into the tomato sauce. Mix well and remove from heat.
Combine Pasta and Sauce: Pour the creamy sausage sauce mixture into the pot with the cooked ziti noodles. Gently fold the sauce into the pasta, ensuring even coating without breaking the noodles.
Assemble the Casserole: Preheat your oven to 425°F (220°C). Lightly grease a 9 x 13-inch baking dish. Spread half of the pasta mixture evenly into the dish. Sprinkle with half of the shredded mozzarella and half of the remaining Pecorino Romano (about 1½ tablespoons). Layer the remaining pasta on top, followed by the rest of the mozzarella and Pecorino Romano cheeses.
Bake Until Golden: Place the baking dish on the middle oven rack and bake uncovered for 15 to 20 minutes. The cheese should melt fully and develop a light golden-brown crust.
Garnish and Serve: Remove the baked ziti from the oven and sprinkle fresh basil over the top. Let it rest for a few minutes before serving warm.