William gives a “thumbs up!” to some soup.

Halve leeks lengthwise and thinly slice crosswise. In a large bowl of cold water wash leeks well and lift from water into a large sieve to drain. In a 6-quart heavy kettle cook leeks in butter over moderately low heat, stirring occasionally, until some begin to turn golden, about 40 minutes. Stir in sugar and cook, stirring occasionally, 10 minutes. Stir in vermouth and cook, stirring occasionally, until liquid is evaporated and most leeks are golden, 10 to 15 minutes. Deglaze kettle with 1/2 cup broth and cook, stirring occasionally, 10 minutes more, until liquid is evaporated and leeks are deep golden. Add remaining 3 cups broth and bring soup just to a boil. Season soup with salt and pepper.