Pour the vinegar into a small, microwaveable bowl and heat on high for 15 seconds. Stir in the cold water.
Place the egg yolks and half the vinegar mixture in a stainless steel bowl and whisk, making circles or figure-8s.
Place the bowl over a saucepan of boiling water, like a double boiler, and turn off the heat. Whisk the mixture without stopping until it starts to thicken and becomes creamy. When the whisk is lifted, the egg should fall back into the bowl in ribbons.
Place the bowl on a work surface and continue whisking. Gently incorporate the butter. Whisk another 2 or 3 minutes. Season with salt and pepper. If the sauce becomes too thick or shiny, add some vinegar mixture. If the eggs and butter don't blend together well, place the bowl over the saucepan again and continue whisking. When the butter and eggs are completely blended, keep the sauce warm until ready to use.
This sauce is ideal spooned over eggs Benedict! Place a slice of Swiss cheese, a slice of white ham, and a poached egg on a toasted English muffin half. Garnish with paprika and snipped chives if you like.