Preheat your oven to 400 degrees. This is a crucial first step to ensure your Baked Ziti cooks evenly and turns golden brown.
Grease a 9-inch-by-13-inch baking dish with olive oil. This will prevent the pasta from sticking and help achieve that perfect crispy top.
In a large stockpot, bring 4 quarts of water and 1 tablespoon of salt to a boil. Once boiling, add the ziti and cook according to the package directions for al dente, which is usually about 10 minutes. After cooking, drain the pasta well.
While the pasta cooks, heat olive oil in a medium saucepan over medium-high heat until shimmering. Add the garlic cloves and sauté until browned, about 3 to 4 minutes. Stir occasionally to prevent scorching. Once browned, remove the garlic and discard it.
Add the ground Italian sausage to the pan and cook until it starts to brown, breaking up clumps with a wooden spoon, about 3 minutes. The sausage should be cooked through and nicely browned.
Next, stir in the crushed tomatoes, diced tomatoes, granulated sugar, dried basil, dried oregano, and salt and pepper to taste. I usually use about ½ teaspoon of salt and ¼ teaspoon of pepper. Let the mixture simmer uncovered for about 10 minutes, stirring occasionally.
Once your sauce is ready, add the cooked pasta to the saucepan and stir to combine everything. Then, fold in the cubed mozzarella, Parmesan cheese, and additional black pepper and crushed red pepper flakes (if using), mixing well.
Pour the pasta mixture into the prepared baking dish, spreading it out evenly. Now, cover the top with the sliced mozzarella and sprinkle with the remaining Parmesan cheese.
Transfer the dish to your preheated oven and bake until the top is lightly browned and everything is hot, which should take about 30 minutes. Keep an eye on it to avoid over-browning!
Once baked, remove the dish from the oven and let it cool slightly. Garnish with minced fresh parsley before serving. Enjoy your homemade Baked Ziti!