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1
Soak the porcini mushrooms in 2 cups warm water for at least 30 minutes.
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2
Lift them out carefully, reserving the liquid.
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3
Rinse porcini well, and pat dry.
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4
Chop coarsely, and set aside.
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5
Strain the soaking liquid through a sieve lined with paper towel to remove the grit.
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6
Set aside.
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7
Bring a large pot of water with 1 tablespoon salt to rolling boil.
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8
Heat the oil and 4 tablespoons of the butter in a large skillet over medium-high heat.
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9
Add the mushrooms, and cook, stirring, until the liquid they release evaporates.
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10
Add the porcini and their liquid, along with the onion, tomatoes and parsley.
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11
Stir.
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12
Partly cover pan, and cook until liquid evaporates.
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13
Season with salt and pepper to taste.
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14
Lay the noodles into boiling water, bring to boil again, and cook 5 to 7 minutes.
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15
Drain immediately, rinse individually under cold running water, and lay flat on paper towels to dry.
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16
Heat oven to 425 degrees.
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17
Melt 8 tablespoons butter in a heavy saucepan over low heat.
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18
Add the flour gradually, and cook, stirring, for 3 to 5 minutes until smooth.
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19
Gradually whisk in milk.
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20
Raise heat to medium, and cook, stirring constantly, until thickened and smooth, about 8 to 10 minutes.
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21
Season with nutmeg, and salt to taste.
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22
Use 1 tablespoon butter to grease 8 1/2-by- 10 1/2-inch lasagna pan.
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23
Line the bottom with a slightly overlapping layer of noodles.
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24
Spread one-third of the mushroom mixture over the pasta.
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25
Top with a quarter of the white sauce and a sprinkling of cheese.
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26
Cover with slices of prosciutto.
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27
Repeat sequence 2 more times.
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28
Cover with one last layer of pasta, top with the remaining sauce and cheese, and dot with 2 tablespoons butter.
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29
Bake 20 to 25 minutes, until the cheese is melted and golden brown on top.
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30
Let stand 10 minutes before serving.
