Active Time

　　2 1/2 hours

　　Total Time

　　12 hours

　　Most people never think about cooking cucumber—especially since that crisp, raw crunch is so perfect for salads and canapés. But cucumber acquires a wonderful velvety texture when cooked and puréed, and this soup shows it off beautifully. Even better, the flavor and color of this soup are at their best when it is warm, not hot, which takes some of the stress out of serving ten guests.

　　

Ingredients

Makes 10 servings

　　3 large seedless cucumbers (usually plastic-wrapped; 3 pounds total), quartered lengthwise and cut crosswise into 1/4-inch-thick slices

　　1 small russet (baking) potato (1/4 pound)

　　1 medium onion, chopped

　　1 medium carrot, chopped (1/2 cup)

　　1/2 celery rib, chopped

　　1 large garlic clove, chopped

　　1 Turkish or 1/2 California bay leaf

　　1 (3-inch) fresh thyme sprig

　　2 tablespoons unsalted butter

　　4 cups water

　　1/4 teaspoon black pepper

　　1 1/2 teaspoons salt

　　Scallop and sole mousselines

　　Garnish: thinly sliced smoked sablefish (black cod); fresh chives or fresh dill sprigs

　　

Step 1

Cook cucumbers in a 4- to 5-quart pot of boiling salted water , uncovered, just until water returns to a boil, about 1 minute, then immediately drain in a colander and transfer to a bowl of ice and cold water to stop cooking. Drain cucumbers well, then purée in 2 batches in a blender until as smooth as possible, about 1 minute, transferring to a bowl.

　　

Step 2

Peel potato and cut into 1/2-inch cubes. Cook onion, carrot, celery, garlic, bay leaf, and thyme in butter in a 2-quart heavy saucepan over moderate heat, stirring occasionally, until vegetables are softened, about 3 minutes. Add potato, 4 cups water, pepper, and 1/2 teaspoon salt and simmer, partially covered, until potato is very tender, about 15 minutes. Discard bay leaf and thyme.

　　

Step 3

Purée mixture in batches in blender until very smooth, about 1 minute (use caution when blending hot liquids), transferring to a large bowl. Chill, uncovered, until completely cool, about 30 minutes.

　　

Step 4

Stir cucumber purée into potato purée and force soup through a fine-mesh sieve into a large bowl, pressing hard on and then discarding solids.

　　

Step 5

Stir remaining teaspoon salt into soup, then reheat in a bowl in a microwave or in a saucepan on stovetop over low heat (microwaving is best because it preserves the soup's bright green color). Put 1 mousseline in each of 10 shallow soup bowls and pour warm soup around each.

　　Cooks' note:

　　Soup can be made 2 days ahead and chilled, covered.