2) Heat the oil in a large frying pan over a medium-high heat. Add the mushrooms and cook, stirring occasionally, until browned and all the liquid has evaporated, about 5 minutes. Season with 1/4 teaspoon of the salt. Stir in 360ml of the tomato sauce and simmer for 2 minutes.
3) In a medium bowl combine the ricotta cheese, spinach, egg, the remaining 1/4 teaspoon salt, a few turns of pepper and the nutmeg.
4) Spread 240ml of tomato sauce on the bottom of a 22cm by 30cm baking dish. Spread about 2 tablespoon of the ricotta mixture onto 1 sheet of lasagna pasta. Top with about 1 1/2 tablespoon of the mushroom mixture, roll the pasta sheet around the filling and place it into the baking dish.
5) Repeat with the remaining sheets of pasta. Spread the remaining 360ml of tomato sauce over the lasagna rolls. Top with the grated cheeses, cover loosely with foil, and bake for 45 minutes. Uncover and bake for 15 minutes more.
For the easy tomato sauce:
1) In a large saucepan, heat the oil over a medium heat. Add the onion and cook, stirring occasionally, until soft, about 5 minutes.
2) Add the garlic and cook for 2 minutes longer. Add the remaining ingredients and cook, uncovered, stirring occasionally, until thickened, about 30 minutes. Season with salt and pepper, to taste.
Yield: 6 servings