Black Truffle Sauce

Wash chopped leek in a bowl of cold water, then lift out and drain (do not pat dry). Steam leek, shallot, and garlic (in any water clinging to leeks) in a 4-quart heavy saucepan, covered, over low heat, stirring occasionally, until softened, about 6 minutes. Add wine, thyme, and truffles and boil, uncovered, until most of liquid is evaporated, about 12 minutes. Add stock and boil until reduced to about 2 cups, about 25 minutes. Stir in cream and simmer, stirring occasionally, until reduced to about 2 3/4 cups, about 40 minutes. Pour mixture through a fine sieve into another saucepan, pressing on and discarding solids. Whisk in truffle oil and season with salt and pepper.