- 2 pounds small (5-inch-long) zucchini
- 1 medium onion, chopped
- 3 tablespoons unsalted butter
- 1 pound boiling potatoes
- 1 teaspoon chopped garlic
- 1/4 teaspoon finely crumbled saffron threads
- 5 cups chicken broth
- 1 Turkish or 1/2 California bay leaf
- 1/2 teaspoon packed fresh thyme leaves
- 1/2 cup chilled heavy cream
- 2 teaspoons fresh lemon juice
- 1 1/4 teaspoons salt
- 1/4 teaspoon black pepper
- 4 large sea scallops (4 ounces total), tough muscle removed from side of each if necessary
- 1 tablespoon vegetable oil
- Special equipment: an adjustable-blade slicer fitted with julienne blade
- Thinly julienne zucchini lengthwise with slicer, working around core, into 1/4-inch-thick ribbons. Cut zucchini cores into 1/2-inch pieces.
- Peel potatoes and cut into 1/2-inch pieces. Cook onion in butter in a 5-quart heavy pot over moderate heat, stirring occasionally, until softened, about 10 minutes. Add potatoes, garlic, and saffron and cook, stirring, 1 minute. Add broth, bay leaf, and thyme and simmer, uncovered, until potatoes are tender, about 20 minutes. Add chopped zucchini cores and simmer, uncovered, until zucchini is very tender, about 8 minutes.
- Purée soup in batches in a blender until very smooth (use caution when blending hot liquids) and pour through a fine sieve into a bowl. Stir in cream, lemon juice, salt, and pepper, then cool to room temperature, uncovered. Chill soup, covered, until cold, at least 4 hours and up to 2 days.
- While soup is chilling, cook julienned zucchini in boiling salted water until crisp-tender, about 30 seconds, then drain and transfer to a bowl of ice and cold water. Drain and pat dry with paper towels. Season with salt and pepper and chill, covered.
- Before serving soup, cut each scallop horizontally into 3 rounds and pat dry. Heat oil in a large nonstick skillet over high heat until hot but not smoking, then sear scallops until golden brown, 20 to 30 seconds on each side, and season with salt.
- Serve soup with zucchini mounded in center, topped with scallop rounds.