A good, creamy lasagna is important to have in your cooking repertoire. This lasagna is simple and easy to make, and the ricotta adds a creaminess that other lasagnas may use béchamel sauce to achieve. The layer of basil adds extra freshness, so be sure to use basil leaves, not dried.
Preheat the oven to 350 degrees.
Heat the olive oil in a medium-sized skillet over medium-low heat. Add the onion and cook until translucent, about 2 minutes. Add the garlic and cook for 1 minute. Add the mushrooms, stir together, and cook until mushrooms are tender, about 4 minutes. Add the spinach and cook until wilted. Set aside.
Meanwhile, bring a large pot of water to a boil and cook the lasagna noodles according to the package directions.
In an 9-by-13-inch baking dish, spread a thin layer of tomato sauce. Cover the tomato sauce with lasagna noodles (you can tear pieces to fill in the edges). Spread the spinach mixture thinly over the noodles. Add a generous layer of ricotta on top of the spinach. Sprinkle mozzarella on top of the ricotta. Put another layer of tomato sauce and repeat the previous process again. Before adding your second layer of mozzarella, cover the entire lasagna with fresh basil leaves. Then, cover with mozzarella and Parmesan.
Place the lasagna in the oven and bake until the cheese is browned on the edges, about 25 minutes.