Step 1 Lightly peel the parsnips and discard the peels. Shave each parsnip with a vegetable peeler, working all the way around the vegetable until you get to its woody core. You'll know you've reached it because it will be rough instead of smooth and ivory-colored. Discard the core and place the shavings in a large bowl. Repeat with the remaining parsnips; you should have about 4 cups, lightly pressed. Discard the cores and reserve the shavings.
Step 2 Melt the butter in a large saucepan or soup pot over medium heat, add the onion and carrot and 1 tablespoon of salt, cover and reduce heat to low. Cook slowly, stirring occasionally, until the vegetables are soft, about 10 minutes. Do not let them scorch.
Step 3Add the shaved parsnips and the potato, cover and continue to cook until the parsnips begin to wilt, about 5 minutes. Add the wine, cover and cook until the vegetables are quite tender, about 20 minutes.
Step 4Add the chicken or vegetable broth, water, the bay leaf, nutmeg, a good grinding of black pepper and salt to taste. Cover and bring to a simmer. Cook until the vegetables are extremely soft, about 20 minutes. You should be able to crush the potato against the side of the pot.
Step 5Discard the bay leaf. Using a slotted spoon, fill a blender about half full with the vegetables. Puree on low speed until coarsely ground. Then, with the motor running, slowly ladle in enough of the broth from the pot to make a smooth puree. Transfer the puree to a large bowl and repeat, using the remainder of the vegetables and broth (it will take about 3 additions).
Step 6Taste and adjust the seasoning. If the parsnips were bitter, you may need to add up to 1 teaspoon sugar to balance it. (The soup can be made up to this point 3 days in advance and refrigerated, tightly covered.)
Step 7When almost ready to serve, return the soup to the saucepan, pouring it through a strainer to remove any grainy bits. Bring to a simmer over medium-low heat.
Step 8In a small bowl, whisk together the egg yolks and the whipping cream until they are smooth. When the puree has reached a simmer, spoon 1/2 cup of it into the cream and egg mixture and whisk until smooth. (This tempers the egg yolks, cooking them slightly so they won't curdle as easily when they're added to the saucepan.)
Step 9Slowly whisk the cream and egg mixture into the puree and continue to cook, whisking frequently, until the soup has thickened slightly and the texture is silken, about 5 minutes. Do not let the soup boil or the egg will curdle. This makes about 9 cups of soup.
Step 1 0Divide the soup among 6 shallow bowls and garnish with the crisp-fried pancetta. Serve immediately.