Before starting, preheat the broiler to high. Wash and dry all produce. Heat Guide for Step 1 (dbl for 4 ppl): 1/8 tsp mild, 1/4 tsp medium and 1/2 tsp spicy! Add 10 cups water and 2 tsp salt to a large pot (use same for 4 ppl). Cover and bring to a boil over high heat. Meanwhile, peel, then cut onion into 1/4-inch pieces. Peel, then mince or grate garlic. Roughly chop parsley. Add half the garlic salt and 1/4 tsp chili flakes to the container with ricotta. (NOTE: Reference heat guide.) Season with pepper, then stir to combine.

Add rigatoni to the boiling water. Cook uncovered, stirring occasionally, until tender, 10-13 min. Reserve 1/4 cup pasta water (dbl for 4 ppl), then drain rigatoni.

Meanwhile, heat a medium oven-proof pan (large pan for 4 ppl) over medium heat. When hot, add 1 tbsp oil (dbl for 4 ppl), then onions. Season with salt and pepper. Cook, stirring occasionally, until tender, 4-5 min.

Add garlic and remaining garlic salt to the pan with onions, then season with pepper. Cook, stirring often, until fragrant, 30 sec. Add crushed tomatoes, broth concentrate and 1/2 tsp sugar (dbl for 4 ppl). Bring to a simmer, then reduce heat to medium-low. Cook, stirring occasionally, until sauce thickens slightly, 6-8 min.

Add rigatoni, spinach, reserved pasta water and half the mozzarella to the pan with sauce. Season with salt and pepper, to taste, then toss to combine. (NOTE: If you don't have an oven-proof pan, for 2 ppl, transfer to an 8x8-inch baking dish. For 4 ppl, transfer to a 9x13-inch baking dish.)Sprinkle with remaining mozzarella, then dollop seasoned ricotta over top. Broil in the middle of the oven until cheese is golden-brown, 3-5 min.

Let rigatoni cool for 5 min. Divide rigatoni between plates. Sprinkle parsley over top. Sprinkle with remaining chili flakes, if desired.