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1
In a small, heatproof bowl, soak the porcini in the boiling hot water until softened, about 15 minutes.
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2
Drain and coarsely chop the porcini.
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3
In a large saucepan, melt 2 tablespoons of the butter in 2 tablespoons of the olive oil.
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4
Add the white mushrooms and the porcini, season with salt and white pepper and cook over moderately high heat, stirring occasionally, until browned, about 10 minutes.
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5
Transfer the mushrooms to a bowl.
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6
Add the remaining 2 tablespoons each of butter and olive oil to the saucepan.
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7
Add the prosciutto and shallots and cook over moderately low heat, stirring occasionally, until softened, about 6 minutes.
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8
Using kitchen string, tie the bay leaf, rosemary, sage and thyme sprigs into a bundle.
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9
Add the herb bundle and the celery root to the saucepan and cook, stirring occasionally, until the celery root is crisp-tender, about 6 minutes.
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10
Add the leeks and cook until the celery root is tender, 5 minutes longer.
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11
Return the mushrooms to the saucepan and stir over moderate heat until hot, 2 minutes.
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12
Add the Marsala and cook until evaporated, 5 minutes.
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13
Pour in 2 cups of the chicken stock and simmer over moderate heat for 10 minutes.
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14
Add 1/2 cup of the cream; simmer for 3 minutes longer, until the mixture has reduced to 5 cups.
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15
Season the ragu with salt and white pepper.
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16
In another large saucepan, combine the remaining 2 cups each of cream and chicken stock and bring to a boil.
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17
Simmer over moderate heat until reduced to 3 cups, about 10 minutes.
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18
Off the heat, whisk in 1 1/2 cups of the Parmigiano-Reggiano cheese.
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19
Whisk in the eggs.
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20
Transfer the sauce to a blender and puree until smooth.
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21
Season with salt and white pepper.
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22
Set 1/2 cup of the sauce aside.
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23
Bring a very large pot of salted water to a boil and fill a large bowl with ice water.
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24
Cook the lasagna noodles until just barely al dente; drain and transfer to the ice water to cool.
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25
Drain the noodles and pat dry.
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26
Preheat the oven to 350.
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27
Butter a 9-by-13-inch baking dish.
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28
Line the bottom with a single layer of noodles, overlapping them slightly; reserve the best noodles for the top layer.
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29
Spread one-fifth of the vegetable ragu on top, followed by one-fifth each of the sauce, mozzarella and basil.
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30
Repeat to make four more layers, ending with a layer of noodles (you won't use all the noodles).
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31
Top with the reserved 1/2 cup of sauce and sprinkle with the remaining 1/4 cup of Parmigiano-Reggiano cheese.
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32
Bake the lasagna until bubbling and golden, about 1 hour.
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33
Let the lasagna rest for 20 minutes before cutting into squares and serving.
