Instructions

1. Lasagna makes great leftovers! You can keep this lasagna in the refrigerator for at least 5 days. Warm up slices in the microwave, or reheat the entire lasagna (covered with foil) in a 350°F oven until the cheese is bubbly.
2. Unbaked lasagna: In the foil-lined pan, assemble the lasagna as directed, but don’t bake it. Cool completely (some of the ingredients will still be warm), then cover with foil and place in the freezer. Once it’s frozen solid, lift it out of the pan, wrap with an additional layer of foil, and freeze for up to 1 month.When you’re ready to bake, unwrap it from the foil and put it back in its original pan. Cover the top with foil and defrost in the refrigerator overnight. Bake as directed in Step 6, allowing an additional 10 to 20 minutes.
3. Baked lasagna: In the foil-lined pan, assemble the lasagna and bake as directed in Step 6. Cool completely, cover with foil, and freeze it until solid. Then lift it out of the pan, wrap it an additional layer of foil, and freeze for up to 1 month.
4. When you’re ready to reheat it, unwrap it and put it back in its original pan. Cover the top with foil (you can reuse the foil use used for wrapping) and defrost in the refrigerator overnight. Reheat covered in foil at 350°F until bubbly again.
5. To substitute fresh spinach for the frozen spinach called for in the ingredients, you’ll need 2 to 3 pounds of fresh spinach to produce 3 cups of chopped, cooked spinach.
6. Soak the fresh spinach leaves in cold water to dislodge any dirt. Remove the from the water and place the wet spinach in a pan, put a lid on, and steam over medium high heat until wilted, about 3 to 4 minutes. You can either chop the spinach before or after you steam it.
7. The first thing I do to start making this recipe is to get a big pot of salted water heating for the pasta and defrost the spinach. While this is happening you can prep the mushrooms and cheeses.
8. If fresh basil is not available for layering in the casserole, add 2 teaspoons of dried basil to the sauce.
9. Set a pot of water over high heat and let it come to a boil while you start the sauce. When the sauce is ready to simmer, the pasta water should be boiling and ready to cook the lasagna noodles.
10. Place mushrooms in a large (6 to 8 quart) sauté pan on high or medium-high heat. Stir them with a wooden spoon or shake the pan from time to time. You may hear them squeak.
11. Sprinkle salt over the mushrooms. The mushrooms will sizzle and then start to release water. (Note that you are not adding fat at this point to the pan; this method of cooking mushrooms in their own moisture is called “dry sautéing”.)
12. Once the mushrooms start to release water into the pan, stir in the chopped onions. Cook until the mushrooms are no longer releasing moisture and the mushroom water has boiled away, about 5 minutes more.
13. Add the olive oil to the mushrooms and stir to coat. Sauté the mushrooms and onions for about a minute. Add the garlic and cook for another minute.
14. Stir in the tomato paste, cook for a minute longer. Reserve 1 cup of the tomato sauce (it will go in the bottom of the casserole dish), and put the remaining cup of tomato sauce into the pot with the mushrooms. Add the large can of crushed tomatoes and one cup of water.
15. Stir in the thyme, sugar, and red pepper flakes. (If you are using dried basil instead of fresh, add it now.) Bring to a simmer, then lower the heat and simmer on a low simmer, for 20 minutes.
16. Spread the one cup of reserved tomato sauce over the bottom of a large (preferably 10- x 15-inch) casserole dish. (If your casserole dish is smaller, you may need to add another layer as you go through this step.)
17. Once the sauce is simmering, salt the boiling pasta water, and add the dry lasagna noodles to the boiling water. (The water should be at a vigorous, rolling boil.) Stir gently, making sure that the noodles are not sticking to each other. Set the timer for 8 minutes, or however long is indicated on the package of the noodles. Cook uncovered on a high boil.
18. When the noodles are ready (al dente, cooked through but still firm to the bite), drain the noodles in a colander, and rinse them to cool them with cold water. As you rinse them, gently separate them with your fingers so they don’t stick to each other.
19. Prepare a couple large cookie sheets or baking sheets by spreading a tablespoon of olive oil over the baking sheets.
20. Place the lasagna noodles on the sheets, gently coating them with a bit of that olive oil, and spreading them out. This will help keep them from sticking to each other while you finish the sauce and prepare the layered casserole.
21. Bake at 350°F for 25 minutes, then remove the foil and bake uncovered for an additional 25 minutes. The cheese should be melted and the sauce bubbling around the edges of the pan.