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1
Thinly julienne zucchini lengthwise with slicer, working around core, into 1/4-inch-thick ribbons.
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2
Cut zucchini cores into 1/2-inch pieces.
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3
Peel potatoes and cut into 1/2-inch pieces.
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4
Cook onion in butter in a 5-quart heavy pot over moderate heat, stirring occasionally, until softened, about 10 minutes.
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5
Add potatoes, garlic, and saffron and cook, stirring, 1 minute.
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6
Add broth, bay leaf, and thyme and simmer, uncovered, until potatoes are tender, about 20 minutes.
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7
Add chopped zucchini cores and simmer, uncovered, until zucchini is very tender, about 8 minutes.
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8
Puree soup in batches in a blender until very smooth (use caution when blending hot liquids) and pour through a fine sieve into a bowl.
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9
Stir in cream, lemon juice, salt, and pepper, then cool to room temperature, uncovered.
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10
Chill soup, covered, until cold, at least 4 hours and up to 2 days.
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11
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.
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12
Drain and pat dry with paper towels.
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13
Season with salt and pepper and chill, covered.
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14
Before serving soup, cut each scallop horizontally into 3 rounds and pat dry.
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15
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.
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16
Serve soup with zucchini mounded in center, topped with scallop rounds.
