1. To make the ragu sauce, heat the oil in a large saucepan over medium heat. Add the onion, celery, carrot, and pancetta and cook for 5 minutes, until softened. Add the beef and cook, breaking up with the side of a spoon, about 10 minutes, until browned.

2. Add the tomatoes and their juices, the wine, and oregano. Bring to a boil, reduce the heat to low, and simmer for at least 40 minutes and up to 2½ hours.

3. Meanwhile, make the white sauce. Melt the butter in a saucepan over low heat, whisk in the flour, and cook for 1 minute. Whisk in the milk. Cook, whisking often, until the sauce boils. Stir in the ricotta. Season with salt, pepper, and nutmeg.

4. Preheat the oven to 375°F (190°C). Oil the baking dish. Spread ¼ cup of the white sauce in the dish. Arrange 3 lasagna in the dish. Top with one third of the ragùand ½ cup of the white sauce. Repeat twice with the lasagna, ragù, and white sauce. Top with 3 lasagna, the remaining white sauce, and the Parmesan.

5. Bake for 45 minutes, until the top is golden and bubbling. Let stand 10 minutes, then serve hot.

Variation:

Vegetarian Lasagna:

Replace the ragu with this vegetable sauce: Sauté 1 chopped onion and 2 chopped celery stalks in 2 tbsp olive oil. Add 2 zucchini, sliced, 1 red bell pepper, seeded and chopped, and 1 small eggplant, cut into small cubes. Sautè for about 20 minutes, until softened and beginning to brown. Add 2 tbsp sun-dried tomato paste, one 14.5 oz (411g) can chopped tomatoes and their juices,1 vegetable bouillon cube, and ¾ cup water. Simmer, partially covered, for 20 minutes.