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1
Whisk mayonnaise, sour cream, and lemon juice in small bowl to blend.
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2
Stir in chopped eggs, capers, parsley, tarragon, and shallot.
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3
Season sauce to taste with salt and pepper.
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4
DO AHEAD Can be made 1 day ahead.
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5
Cover and refrigerate.
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6
Cut off bottom 1 inch from each asparagus spear.
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7
Using vegetable peeler, peel each spear from about 2 inches below tip to base to remove stringy outer layer.
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8
Bring large saucepan of salted water to boil.
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9
Squeeze juice from 1/2 lemon into boiling water; add lemon half, butter, and sugar.
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10
Add asparagus and cook just until tender when pierced with knife or skewer, 5 to 8 minutes, depending on thickness and color.
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11
Using slotted spoon or tongs, remove asparagus from saucepan and transfer to platter to cool.
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12
DO AHEAD Can be made 1 day ahead.
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13
Cover; chill.
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14
Just before serving, add 3 tablespoons olive oil to sauce and stir without overmixing (sauce should have coarse texture and olive oil should be slightly separated).
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15
Arrange asparagus decoratively on platter or individual plates.
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16
Drape salmon slices over.
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17
Spoon a few tablespoons sauce over; drizzle lightly with additional olive oil.
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18
Serve, passing remaining sauce alongside.
