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1
In a small saucepan combine vinegar, wine, shallots, and dried tarragon and simmer over moderate heat until reduced to 2 tablespoons of liquid.
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2
Cool and strain through a fine sieve.
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3
In the top of double boiler or a heat-proof bowl whisk the egg yolks until they become thick and sticky.
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4
Whisk in the reduced vinegar mixture and pepper.
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5
Place the pan or bowl over a saucepan of simmering, not boiling, water.
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6
Whisk until mixture is warm, about 2 minutes.
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7
(If mixture appears to become lumpy, dip pan immediately in a bowl of ice water to cool, whisk until smooth and then continue recipe.)
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8
The yolk mixture has thickened enough when you can see the bottom of the pan between strokes and mixture forms a light cream on the wires of the whip.
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9
While whisking the yolk mixture gradually pour in the melted butter, a tablespoon or so at a time whisking thoroughly to incorporate before adding more butter.
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10
As the mixture begins to thicken and become creamy, the butter can be added more rapidly.
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11
Do not add the milk solids at the bottom of the melted butter.
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12
Season the sauce, to taste, with chopped tarragon, salt and pepper.
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13
To keep the sauce warm, set the pan or bowl in lukewarm water or in a thermos.
