Preheat and prep: Heat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Brown the sausage: In a skillet over medium heat, warm the olive oil.
Add the sausage and cook, breaking it up, until browned and cooked through, 5–7 minutes. Stir in the garlic for 30 seconds. Remove from heat.
Build the sauce base: In a large bowl, whisk together marinara, chicken broth, cream, Italian seasoning, and red pepper flakes.
Taste and season with salt and pepper.
Combine in the baking dish: Add the uncooked ziti to the dish. Pour in the sauce mixture. Add the cooked sausage, 1 cup mozzarella, Parmesan, and dollops of ricotta.
Stir gently to distribute.
Cover and bake: Cover tightly with foil. Bake for 30 minutes, until the pasta is mostly tender and the sauce is bubbling.
Add cheese and finish: Remove foil, sprinkle the remaining 1 cup mozzarella on top, and bake uncovered for 10–15 minutes until the cheese is melted and lightly browned.
Rest and serve: Let the ziti rest for 5–10 minutes so the sauce sets. Garnish with chopped basil or parsley and extra Parmesan.
Serve warm.