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1
In a large saucepan, melt 1 tablespoon of the butter.
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2
Add the pancetta and cook over moderate heat until lightly browned, about 5 minutes.
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3
Add the shallots and celery root and cook until the celery root is just tender, about 10 minutes.
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4
Transfer the vegetables to a bowl, leaving the pancetta and fat in the saucepan.
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5
Add the remaining 1 tablespoon of butter to the saucepan along with the mushrooms and all but 2 tablespoons of the chestnuts.
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6
Cook over moderately high heat, stirring occasionally, until the mushrooms have released their liquid and are slightly softened, 6 minutes.
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7
Add 2 tablespoons of the chicken stock and the celery root mixture and cook for 1 minute.
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8
Add the Cognac and cook until evaporated, 2 minutes.
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9
Add the bay leaf, sage and thyme sprigs to the saucepan along with the remaining 3 3/4 cups plus 2 tablespoons of chicken stock.
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10
Bring to a boil and simmer for 30 minutes, stirring occasionally.
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11
Discard the pancetta, bay leaf, sage and thyme.
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12
Working in batches, puree the soup in a blender until creamy and smooth.
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13
Return the soup to the saucepan.
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14
Stir in the half-and-half, season with salt and white pepper and keep warm.
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15
In a large bowl, using a handheld electric mixer, whip the cream until soft peaks form.
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16
Beat in the grappa and season with salt and pepper.
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17
Ladle the soup into small bowls.
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18
Dollop the grappa cream on top, garnish with the thyme leaves and the reserved 2 tablespoons of chestnuts and serve.
