Preheat the oven to 350F.

2. Make the tomato sauce: In a medium pot, heat the olive oil and add the onions and garlic. Season with salt. When it turns light brown, add the thyme, bay leaf and tomatoes. Simmer for 20 minutes. Taste for seasoning. Add more salt and pepper, if desired. Remove and discard the thyme and bay leaf. Stir in the basil leaves and shut off the heat to allow the sauce to “rest.”
3. Cook the pasta: bring the water to a boil. Add a generous handful salt and the lasagna sheets. Cook for 4 minutes, stirring so they don’t stick, drain and rinse under cold water. The pasta should still be very firm to the touch. Separate the sheets carefully so they don’t stick together.
4. Assemble the lasagna: Spoon a thin layer of the sauce in the bottom of the baking pan. Arrange a layer of pasta sheets over the sauce. Sprinkle some of the spinach leaves, mozzarella and Parmesan cheese over the pasta and another thin layer of sauce. Repeat the layering process 2 more times. It is important there be remaining cheese and sauce for the top. I love to get a corner piece from the pan and pick at the crispy edges of the top layer…when you finish, there should be 3 layers of pasta and 4 layers of filling.
5. Bake: Cover the dish tightly with aluminum foil and place in the center of the oven. Bake for 45 minutes. Raise the temperature of the oven to 450F and remove the aluminum foil. Bake additional 10-15 minutes or until the top browns slightly. Remove from the oven. Cool and refrigerate.

Serve: Serve whole and cut into slices. Alternatively, cut into 1-inch slices and arrange, overlapping, in a baking dish with a splash water and sauce. Bake in a 350F oven 25-30 minutes or until hot.