1. Fill a 9-by-13-inch baking dish two-thirds of the way with hot tap water. Add noodles, and arrange them in alternating directions to prevent sticking. Let soak while preparing sauce.

2. Make sauce: Heat oil in a large saucepan over medium. Add onion, garlic, Italian seasoning, and red-pepper flakes; cook, stirring occasionally, until lightly browned, about 5 minutes. Add sausage, and cook, stirring and breaking it up, until just cooked through, about 5 minutes. Add tomatoes and their puree, breaking up tomatoes with a spoon; bring to a boil. Reduce to a rapid simmer, and cook, stirring occasionally, until thickened, about 20 minutes. (You should have about 8 cups of sauce.) Season with salt and pepper.

3. Preheat oven to 350 degrees. Drain noodles, transfer to a baking sheet; dry dish with paper towels. Spoon 1 cup sauce in bottom of dish. Fit 4 noodles in dish (crosswise if using short noodles, lengthwise if using long), overlapping slightly. Cover with 2 cups sauce, 2 cups mozzarella, and 1/4 cup Parmesan. Repeat with another layer, then top with remaining noodles, 3 cups sauce, and the rest of mozzarella and Parmesan. Cover dish tightly with aluminum foil, and bake 1 hour.

4. Remove foil, and continue baking until bubbly and browned, about 30 minutes. Remove from oven; let cool 20 minutes. Cut and serve.