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1
Preheat oven to 350F.
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2
Whisk together sour cream and lemon juice.
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3
Add oil in a slow stream, whisking until emulsified.
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4
(If necessary, add water, 1/2 tablespoon at a time, for a thick yet spoonable consistency.)
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5
Stir in chives, tarragon, salt, and pepper to taste.
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6
Soak onion in cold water to cover 10 minutes, then drain and pat dry.
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7
Halve and peel avocados and cut crosswise into 1/4-inch-thick slices, then sprinkle slices with lemon juice.
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8
Put 2 brioche toasts on each of 8 plates and season with salt and pepper.
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9
Arrange a few sorrel leaves on each toast, then top with avocado and onion.
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10
Fill a well-buttered 17- by 11- by 2-inch flameproof baking pan with 1 1/4 inches water and stir in vinegar (to help whites coagulate faster).
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11
Set pan to straddle 2 burners and bring water to a simmer.
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12
Break 1 egg into a cup and slide into water.
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13
Repeat with remaining eggs, adding them in rows so you can easily take them out in same order.
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14
Poach eggs at a bare simmer 3 to 4 minutes, or until whites are firm but yolks are still runny.
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15
Transfer eggs as cooked with a slotted spoon to kitchen towels to drain and season with salt and pepper.
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16
Wrap each egg in a slice of salmon.
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17
Put a wrapped egg on top of each toast and drizzle sauce over salmon.
