This savoury soup can be made 2 days ahead and cooled completely, uncovered, then chilled, covered. Reheat, adding more water if necessary to thin to desired consistency.
2 leeks (white and pale green parts only), chopped (1 cup)
3 medium red onions, chopped (3 1/2 cups)
1/2 lb fennel bulb (sometimes called anise), stalks discarded and bulb cored and chopped (1 1/4 cups)
1 large garlic clove, minced
2 tablespoons unsalted butter
60ml (1/4 cup) dry white wine
500ml (2 cups) vegetable stock or low-sodium chicken broth
310ml (1 1/4 cups) water
1 teaspoon salt
1/4 teaspoon black pepper
1/8 teaspoon freshly grated nutmeg
250ml (1 cup) heavy cream
2 teaspoons Pernod (anise flavoured aperitif)
Garnish: chopped fresh chives
Wash leeks well in a bowl of cold water, then lift out and drain well.
Cook onions, leeks, fennel, and garlic in butter in a 5- to 6-quart heavy pot over moderate heat, covered, stirring occasionally, until softened, about 15 minutes. Add wine and boil, uncovered, until evaporated, about 1 minute. Add stock, water, salt, pepper, and nutmeg and simmer, uncovered, until vegetables are tender, about 10 minutes. Stir in cream and simmer, stirring occasionally, until slightly thickened and liquid is reduced to about 6 cups, about 15 minutes.
Purée soup in batches in a blender until smooth (use caution when blending hot liquids), then transfer to a soup tureen and stir in Pernod.