A pasta al forno dish using ziti.
Create a béchamel using the butter, flour, milk, and 2 cups Parmesan. Set aside.
Heat oil in a large saucepan over medium-high. Cook pancetta, stirring often, until golden brown, 2 minutes. Add onion, garlic, and red pepper flakes; season with salt and pepper. Cook, stirring often, until onion is golden and soft, 8–10 minutes. Add tomato paste and cook, stirring, until slightly darkened, 2 minutes.
Add tomatoes, crush, and season with salt and pepper. Bring sauce to a simmer and cook, stirring often, until slightly reduced and flavors have melded, 20–25 minutes. Let cool slightly, blend until mostly smooth. Stir in basil and season with salt and pepper.
Meanwhile, preheat oven to 350°F. Transfer béchamel to a large bowl; add pasta and mozzarella and toss to combine. Add all but 1 cup tomato sauce and gently fold mixture a few times, leaving streaks of béchamel.
Transfer pasta to a 13x9" or other 3-quart baking dish, dollop with remaining tomato sauce, and scatter remaining Parmesan over pasta. Bake until mozzarella is melted and sauce is bubbling around the edges, 15–20 minutes.
Broil until pasta and cheese are dark brown in spots, 4 minutes. Let sit 5 minutes before serving.
Omitted the basil and pancetta; used fusilli instead of ziti. Something is wrong with the tomato sauce to cheese sauce recipe - the scale may be dying. There is too much cheese to tomato, but it is still good. 1/4 tsp. salt is definitely not enough, at least double it next time.
Added at least 2 tsp. salt, plus about 1/2 tsp. Baking soda to counteract the acidity of the tomato. Omitted pancetta. Still needed to add additional salt to individual portions, but once salted this is good as always.