You will need:
16 lasagna noodles (4 layers)
4 cups milk
1 stick butter (I used salted, if you use unsalted, add more salt to your sauce)
1/2 cup flour
About 3/4 tsp. kosher salt
About 1/2 tsp. fresh ground pepper
1/2 teaspoon fresh ground nutmeg
3 garlic cloves, minced
3 tablespoons chopped Italian parsley
1 tablespoon chopped fresh thyme leaves
4 tbsp. olive oil, divided
1/2 an onion, diced (or two medium leeks sliced into rings)
1 1/2 pounds portabella mushrooms, sliced
1/2 pound shiitake mushrooms, stemmed and sliced
1 cup finely grated fresh parmesan cheese
Determine how many noodles it takes to make a layer in your pan and multiply by 4. Soften noodles in a pot of very hot (but not boiling) water. Noodles should be soft but not fully cooked.
Make béchamel sauce: Bring milk to a simmer in a small saucepan and remove from heat. Melt butter in a large saucepan over medium heat. Whisk in four until slightly browned, about 2 minutes. Whisk in milk all at once, keep whisking until smooth. Add salt, pepper, and nutmeg. Sauce should be thick enough to coat a spoon, if too thick add more milk, if too thin, cook over medium-low heat, stirring, until thickened. Remove from heat and stir in garlic, 1/2 tbs. thyme and most of the parsley (leave some to sprinkle on dish after it bakes).
Preheat oven to 375°. Heat a deep, wide pot over medium-high heat. Add 2 tbsp. olive oil. Sauté the onion (or leeks if you have them) until translucent, set aside. In the same pot, add the remaining olive oil and sauté mushrooms, covered, until mushrooms are tender and beginning to release juices, about 5 minutes. Lightly salt and pepper mushrooms. Uncover and cook until edges start to brown. Stir in the cooked onion and remaining 1/2 tsp. thyme.
Assemble lasagna: Lightly oil a 9-by-13-in. baking dish. Spread a few spoonfuls of béchamel over bottom. Add a layer of noodles, then spoon on a layer of béchamel sauce (about 1/2 cup), followed by a third of the mushrooms and third of the cheese. Repeat layers twice more. Top with a final layer of noodles and remaining béchamel and sprinkle with the rest of the cheese.
Bake lasagna until browned and bubbling, about 45 minutes. Sprinkle with remaining parsley and let sit for 15 minutes before slicing. Pair with chilled Lambrusco (Trader Joe's has a good one).
Recipe adapted from here. (Warning, this recipe creates a mountain of dishes. And in our case they are still waiting to be washed...)