2 ounces dried porcini mushrooms
2 sticks ( 1/2 pound) plus 1 tablespoon unsalted butter
3 1/2 tablespoons olive oil 4 large shallots, minced
2 pounds fresh white button or cremini mushrooms, minced
1 1/2 teaspoons chopped fresh tarragon or 1/2 teaspoon dried
1 1/2 teaspoons salt
1/2 teaspoon freshly ground black pepper
4 tablespoons fresh lemon juice
2 small garlic cloves, minced
3/4 pound fresh shiitake mushrooms, stemmed, caps sliced 1/4 inch thick
1/2 cup all-purpose flour
2 cups milk
1 cup heavy cream
1/4 pound Gorgonzola dolcelatte cheese
3/4 cup freshly grated imported Parmesan cheese (about 3 ounces)
Homemade Lasagne Noodles or 1 package (16 ounces) lasagne noodles
In a medium bowl, cover the porcini with 3 cups boiling water. Let stand until softened, 20 to 30 minutes. Lift out the mushrooms; reserve the liquid. Coarsely chop the porcini. Strain the liquid through a double layer of cheesecloth and reserve 2 cups.
Meanwhile, in a large heavy skillet, melt 2 tablespoons of the butter in 1 tablespoon of the olive oil over moderately high heat. Add 2 tablespoons of the minced shallots and half the minced fresh mushrooms. Sauté, stirring frequently, until the mushrooms give up their liquid, it evaporates, and the mushrooms become lightly browned, 5 to 7 minutes. Season these mushroom duxelles with half the tarragon and 1/4 teaspoon each salt and black pepper, a dash or two of cayenne, and 1 tablespoon of the lemon juice. Scrape into a bowl. Wipe out the skillet with a paper towel. Repeat with 2 more tablespoons of the butter and 1 tablespoon olive oil, adding 2 more tablespoons of the shallots and the remaining minced fresh mushrooms. Season as above. Add to the bowl. Wipe out the skillet.
In the same large skillet, melt 3 tablespoons of the butter in the remaining 1 1/2 tablespoons oil over moderately high heat. Add the remaining minced shallots and the garlic and sauté for 30 seconds. Add the shiitake and porcini mushrooms and sauté, stirring frequently, for 3 minutes. Reduce the heat to moderately low and cook, stirring frequently, for 5 minutes. Add 1 cup of the reserved porcini liquid and simmer, partially covered, for 5 to 10 minutes, until the mushrooms are tender but still slightly chewy. Uncover and cook, stirring frequently, until the remaining liquid evaporates. Season with the remaining 2 tablespoons lemon juice and salt and pepper to taste. Add to the mushroom duxelles and set aside.
In a large heavy saucepan, melt 1 stick of butter over moderate heat. Add the flour and cook, stirring, for 2 to 3 minutes without letting the flour color. Whisk in the remaining 1 cup mushroom liquid, the milk, and the cream. Bring to a boil, whisking constantly, until thickened and smooth. Reduce the heat and simmer, whisking frequently, for 5 minutes. Turn off the heat. Whisk in the Gorgonzola and 1/2 cup of the Parmesan cheese until melted. Season with 1 teaspoon salt and several dashes of cayenne.
In a large pot of boiling salted water, cook the lasagne noodles until just tender, about 1 minute after the water returns to a boil for fresh noodles, about 12 minutes for the dried variety. Drain and rinse under cold running water. Place in a bowl of cold water and, one by one, lay the noodles out in a single layer on kitchen towels to dry.
To assemble the lasagne, generously butter 2 large baking pans, 9 × 13 × 2 inches. If the sauce has cooled, reheat it slightly over low heat. Arrange a layer of noodles in the bottom of each dish, trimming to fit, if necessary, and overlapping the edges only slightly. Spread a thin layer of mushrooms over the noodles (using one-quarter of the total amount in each pan) and drizzle about 1 cup of sauce over the mushrooms in each pan. Repeat with another layer of noodles, mushrooms, and sauce. Top with a final layer of noodles. Spread the remaining sauce over the noodles, dividing evenly, and divide the remaining 1/4 cup grated Parmesan cheese evenly over the tops. Dot each with 1 tablespoon butter. (The lasagne can be assembled completely and refrigerated, covered, overnight or frozen for up to 2 weeks.)
Heat the oven to 375°F. Bake the lasagne (thawed, if frozen) uncovered for 20 to 30 minutes, until heated through and lightly browned on top.