Preheat the oven to 350°F. Lightly grease a 9×13″ baking dish.
In a large saucepan over medium heat, cook and stir the beef and onion, until the beef is browned and the onion has softened, about 5 minutes. Drain any juices released.
Add the Italian seasoning, garlic, salt, chili flakes (more or less according to your tastes), and pepper and cook for 1 minute.
Add the sauce and cook for 5 minutes, stirring occasionally. Taste, adjust seasonings, and set aside.
Meanwhile, bring a large pot of water to a rolling boil over high heat. Salt well and add the rigatoni. Reduce the heat to medium-high and cook according to package directions, just until al dente.
Drain the pasta, reserving ½ cup of the water. Stir the reserved pasta water into the sauce.
In the saucepan, combine the pasta and sauce. Pour the mixture into the prepared baking dish.
Sprinkle with the mozzarella and Parmesan and bake for 15 to 20 minutes, or until heated through and the cheese has started to brown.
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Notes
**Optionally, cover and refrigerate up to 2 days. Bake at 350 degrees F until heated through, about 30-40 minutes.Ingredients and Substitutions:Ground Beef: feel free to swap the ground beef for ground Italian sausage (mild or spicy according to your tastes), or ground pork, chicken or turkey.Vegetables: onion provides a great flavor base for our sauce, but this is also a great time to add in other vegetables. Finely chopped or shredded carrots, mushrooms, peppers, zucchini, celery and more are great additions. You can also stir some spinach into the sauce after simmering.Rigatoni: this recipe works just as well with any cut of pasta! Feel free to use what you have on hand. I often use a whole grain variety.