Step1
Place the white wine, white wine vinegar, parsley, tarragon stems, shallots, peppercorns and red pepper flakes in a saucepan and bring to a simmer.
Step2
Simmer until liquid has reduced to 1/2 c., and then strain the liquid into another container.
Step3
Meanwhile, bring about two inches of water to a simmer for a double boiler.
Step4
Melt the butter in a small saucepan over low heat until completely melted.
Step5
Skim off and discard the white foam that rises to the top. Ladle off and reserve the clear yellow liquid in the middle (this is clarified butter) and discard the milky liquid that has fallen to the bottom.
Step6
Place the egg yolks in a medium metal bowl or in the bowl of a double boiler and whisk together.
Step7
While whisking the egg yolks continuously, place the bowl over the simmering water for about 20 or 30 seconds, and then remove it and whisk for a few seconds. Repeat. The key is to heat the yolks up slowly so that they don't scramble. If they scramble, you'll need to start over.
Step8
Keep whisking until the yolks get firmer. Look for the ribbon stage, when they're firm enough that you can lift the whisk out of the yolks and drizzle some back onto the surface, forming a ribbonlike pattern that lasts for a few moments before sinking back into the yolks.
Step9
When this stage is reached, slowly drizzle in some of the melted clarified butter while whisking constantly.
Step10
When a ladle or two of butter has been added, begin alternating between the melted butter and the vinegar mixture.
Step11
When the mixture has thickened and begins resembling a sauce, season with salt, add the chopped tarragon and parsley leaves and begin tasting. If too sour, whisk in more melted butter. If not tart enough, squeeze in some lemon juice. If too thick, whisk in some hot water.
Step12
Keep in a warm place until ready to use. The sauce will thicken as it sits.