Makes about 3/4 of a cup. Recipe is from Viking Cooking School Outdoors and Carnevino Restaurant, Las Vegas.
1/4 cup champagne vinegar
2 tbls. finely minced shallots
1/2 oz. dried porcini mushrooms
2 tsps. minced fresh tarragon, divided
3 large egg yolks
1 tbl. water
2 to 3 tbls. unsalted clarified butter, warm
Salt and freshly ground black pepper, to taste
1/2 cup finely diced fresh porcini mushrooms
1. Combine the vinegar, shallots, dried mushrooms and 1 teaspoon of the tarragon in a small sauce pan. Place over medium-low heat and simmer until the liquid is reduced by half. Remove from the heat and set aside to steep for 10 to 15 minutes. Strain through a fine mesh strainer, pressing on the solids to extract as much flavor as possible; discard the solids and set the liquid aside.
2. Fill a double boiler or small sauce pan half-full with water and set over medium heat. Bring it to a simmer. In the top of the double boiler or in a mixing bowl, whisk egg yolks and water until creamy and smooth.
3. Place the mixture over simmering water. The water should not touch the bottom of the bowl. Cook, whisking constantly until the eggs have increased in volume and have begun to thicken to a smooth sauce.
4. Slowly whisk in the clarified butter, adding it in a thin, steady stream. Alternate with the porcini-infused vinegar until a creamy emulsion forms. Remove from the heat and stir in the diced fresh mushrooms. Season to taste with salt and pepper. Hold in a warm water bath or a thermos until needed. Just before serving, stir in the minced fresh tarragon.
Note: Clarified butter is pure butterfat which has had the milk solids removed. To clarify butter, melt the butter in a heavy sauce pan over medium-low heat. Continue cooking until the butterfat becomes very clear and the milk solids drop to the bottom of the pot. Skim the surface foam as the butter clarifies. Ladle off the butterfat into another container, being careful to leave the milky residue in the bottom of the pan. It is much easier to clarify at least one pound of butter at a time. One pound of whole butter yields about 12 ounces of clarified butter.