Make marinara sauce and wild mushroom-leek mix in advance. They can be made the day before if desired.
When ready to assemble: Preheat oven to 350 degrees. Coat 12 x 16 x 2 1/2-inch pan with vegetable oil spray, then layer ingredients.
For first layer: Add 7 lasagna noodles, 3 1/2 cups marinara sauce, half the spinach, a third of the mozzarella cheese.
For second layer: Add another 7 lasagna noodles, all the mushroom leek mixture, all the Parmesan cheese.
For third layer: Add another 7 lasagna noodles, another 3 1/2 cups marinara sauce, the remaining spinach, another third of the mozzarella.
For fourth layer: Add 7 lasagna noodles, remaining marinara sauce and remaining mozzarella cheese. You may have leftover noodles; save for another use.
Cover pan with foil and bake in preheated oven 1 hour. Uncover and let rest 5 minutes before cutting and serving.
Note: Leftovers freeze well. Wrap individual portions, then freeze.
To serve, thaw in refrigerator, then reheat 1 to 2 minutes in the microwave on full power.
In large saucepan over medium heat, add oil. Sauté onion, celery, carrot, garlic and crushed red pepper 10 minutes, stirring often.
Add diced tomatoes and tomato puree, mix well, reduce heat to low and simmer 2 hours, stirring occasionally. Transfer to container, add pesto, salt and pepper. Refrigerate uncovered.
After mixture has cooled completely, puree in food processor, then return to container, cover and refrigerate. Sauce can be made 2 to 3 days before making lasagna.
Cover porcini mushrooms with water, cover and set aside until soft.
Roughly chop leeks and fresh mushrooms.
In large sauté pan, add 1 tablespoon of the oil. Add leeks and garlic and sauté 3 minutes. Season with some salt and pepper. Remove from heat and transfer to large cookie sheet.
In same pan over medium-high heat, add another tablespoon oil and add half the mushrooms. Sauté until they just start to release their liquid. Season with some of the salt and pepper and half the fresh herbs. Remove from heat and place on cookie sheet with the leeks.
Repeat same process using remaining tablespoon oil, mushrooms and herbs. Remove porcini mushrooms from liquid and add to mushroom mixture in pan. Drain soaking mixture through coffee filter, making sure to leave sand and grit behind. Sauté another 3 minutes. Transfer last batch of mushrooms to same cookie sheet and refrigerate. When cool, place in container and mix well. Cover and refrigerate until ready to use.Makes 4 Source: