What's old-fashioned about this lasagna is that it contains the holy trinity of ricotta, mozzarella, and tomatoes
1/3 cup olive oil
3 large yellow onions, diced (about 3 cups)
three 28-ounce cans plum tomatoes, drained
1 tablespoon coarse salt
1 teaspoon freshly ground black pepper
2 cups whole-milk ricotta
2 tablespoons plus 1/2 cup finely grated Parmigiano-Reggiano
1 tablespoon chopped fresh basil
1/8 teaspoon freshly grated nutmeg
3 tablespoons butter, melted
18 sheets lasagna, each about 10 inches by 2 inches, parboiled
1 pound mozzarella, grated (about 3 cups)
1. Heat olive oil over moderate heat in large saucepan. Add onions, stir, and cover. Cook for about 20 minutes, stirring occasionally, until onions are translucent. Using a food mill, purée plum tomatoes directly into the pan. Add 2 teaspoons of the coarse salt and 1/2 teaspoon of the pepper, and cook, uncovered, for about 30 minutes, or until sauce is reduced to about 41/2 cups.
2. In small bowl mix ricotta, egg, 2 tablespoons of the Parmigiano-Reggiano, basil, remaining salt and pepper, and nutmeg. Stir well to combine.
3. Butter generously the bottom and sides of a baking pan, 11 inches by 9 inches by 1 1/2 inches. Take 3/4 cup of tomato sauce and spread on bottom of pan.
4. Place 3 lasagna noodles on bottom of pan, overlapping them slightly. Spread a heaping 1/3 cup of ricotta mixture evenly over noodles. Spread 3/4 cup of tomato sauce on top of this. Sprinkle with a heaping 1/3 cup of mozzarella. Repeat this 4 times. Then place last 3 noodles on top and sprinkle with remaining mozzarella and remaining 1/2 cup of Parmigiano-Reggiano. (The lasagna may be assembled up to this point 2 days in advance and stored in refrigerator, covered. Bring to room temperature before cooking.)
5. When ready to cook, preheat oven to 400 degrees. Bake on top shelf of oven for 20 to 25 minutes, or until cheese is melted. Let sit for 5 minutes and serve.
What's old-fashioned about this lasagna is that it contains the holy trinity of ricotta, mozzarella, and tomatoes. However -- unlike the prototypical Italian-American lasagna, which is so heavy and oozy with cheese that it sags under its own weight -- this lasagna comes closer to the Italian lasagna ideal of lightness, simplicity, and what Marcella Hazan calls deftness. You could increase the mozzarella by 50 percent if you want the dish heavier, or you could add sausage and/or meatballs in the classic Little Italy manner. But we prefer this vegetarian lasagna just as it is, with its great purity of tomato flavor. Serves 6