1/2 pound (2 sticks) unsalted butter
4 shallots, finely chopped
2 tablespoons fresh tarragon leaves
4 white peppercorns, crushed
1/4 cup white wine vinegar
1/3 cup dry white wine
4 large egg yolks
1/4 teaspoon salt
Pinch of cayenne

Heat the butter in a medium saucepan over medium heat just to melt. Boil shallots, tarragon, and peppercorns in vinegar and wine in a nonreactive medium-size saucepan over medium heat until reduced to about 1/4 cup. Strain into the top of a double boiler. Whisk in the egg yolks. Bring water in lower part of double boiler to simmer and place upper part on the lower. Make sure that the surface of the water is below the bottom of the upper part of the double boiler. Whisk constantly. The second that the yolk mixture begins to thicken slightly, remove the top of the double boiler from above the hot water and continue whisking. Turn off the heat. Add four ice cubes to the bottom of the double boiler to cool the hot water a little. Put the pan of yolks back above the hot water. Whisk in the melted butter, drizzling it in very slowly. If at any time the sauce looks as if it is about to break, remove the top and continue whisking to cool it down or whisk in 1 teaspoon cold water. With constant whisking, whisk in the salt and cayenne. When all the butter is incorporated, taste and add more salt or cayenne as needed.