Instructions

1. Arrange a rack in the middle of the oven and heat the oven to 350°F.
2. Bring a large pot of heavily salted water to a boil over high heat. Meanwhile, prepare the aromatics, cheese, and sausage.
3. Dice 1/2 medium yellow onion (about 1/2 cup). Mince 4 garlic cloves. Cut 1 pound mozzarella cheese into 1/2-inch cubes (about 3 cups). Finely grate 2 ounces Parmesan cheese (about 1 packed cup), or measure out 2/3 cup store-bought grated. Remove the casings from 1 pound Italian sausage if needed.
4. Heat 2 tablespoons olive oil in a large skillet over medium heat until shimmering. Add the onion and cook until softened, 3 to 4 minutes. Add the garlic and cook until fragrant, 30 seconds to 1 minute.
5. Add the sausage, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper. Cook, breaking up the sausage with a wooden spoon or spatula into small pieces, until browned and cooked through, 6 to 8 minutes. Add 1 jar of the marinara sauce (about 3 cups) and stir to combine, scraping up any browned bits from the bottom of the pan. Remove the pan from the heat.
6. Add 1 pound rigatoni pasta to the boiling water and cook according to package directions for 2 minutes less than al dente, about 8 minutes. Drain the pasta and return it to the now-empty pot off the heat.
7. Add the sausage mixture and remaining 1 jar marinara sauce to the pasta and stir to combine. Add half of the mozzarella and fold it in.
8. Transfer the mixture to a 9x13-inch baking dish, or divide between 2 (8-inch) baking dishes or disposable foil trays. (Use a metal or disposable baking dish if you’re planning to freeze this.) Sprinkle with the remaining mozzarella and Parmesan.
9. Bake until the edges are bubbling and the cheese on top is completely melted and browned in spots, about 30 minutes. Let cool for 5 to 10 minutes before serving. Garnish with chopped fresh parsley leaves if using.