For the ragu:
Add the porcini mushrooms in 1 cup hot water, sork until soft, 20 minutes.
Strain through a fine-mesh sieve over a bowl or a measuring cup.
Chop the re dehydrated mushrooms and reserve the soaking liquid. Set aside.
While the mushrooms are soaking, add the olive oil in a dutch oven or a large pot over medium heat, heat until hot.
Add the onion, and cook until soft and become brown, about 8 minutes or longer.
Stir in the carrots and celery, and cook for another 3 to 5 minutes until the vegetables are soft.
Add the garlic and tomato paste, stirring, and cook for another 2 to 3 minutes.
Stir in the mushrooms, salt and black pepper to taste.
Cook, stirring, until the mushrooms are soft and some of the moisture has been evaporated, about 8 minutes.
Stir in the chopped porcini mushrooms, and cook for about 3 minutes.
Pour the reserved porcini soaking liquid, bring the pot to a boil and cook the sauce until thickened a bit, 4 to 6 minutes.
Pour in the tomatoes and the juice, and the bay leaves.
Bring to a boil, stirring two or three times.
Reduce the heat to medium low, add the Italian seasoning mix, stirring about three times, until thick, about 1 hour or more.
Discard the bay leaves.
Note: The sauce can be made 1 day ahead, allow to cool, then cover with a plastic wrap and put in the frige. Reheat before using.
Meanwhile wilt the washed spinach leaves with some water on the leaves in a large pan or pot until the leaves are all witled, 3 to 5 minutes.
Let cool enough to handle, transfer the spinach into a stainer, sieve or colander, squeeze the excess water, then chop the spinach.
For the lasagna filling:
Add the parmesan, mozzarella and cheddar in a medium bowl; mix until well combined.
Reserve 1 cup of the cheese mixture and set aside.
In a large mixing bowl, add the remaining cheese mixture, ricotta cheese, egg, spinach, nutmeg and 1/4 teaspoon salt. Mix until well blended.
Preheat the oven to 375 degrees F.
Bring a large bot of salted water to a boil.
Cook the lasagne noodles according to the directions on the box.
Drain and rinse under cold water, shake off the excess water.
Spread 1 cup of the ragu in a 9-by-13-inch baking dish.
Arrange three lasagna noodles, then half of the spinach mixture and 2 cups ragu.
Place another three lasagna noodles, then the remaining spinach mixture and another 2 cups ragu.
Top with last 3 noodles and remaining ragu and sprinkle the reserved cheese over.
Cover with a large piece of foil, try to not touch the cheese.
Put on a baking sheet and bake 50 minutes.
Take off the foil and bake until golden, 20 to 25 minutes or more.
Allow to rest for at least 15 minutes before serving.
Slice and serve warm.
