Place the butter in a pan and clarify it to separate the milk solids and fat. Keep it at room temperature.

(Reduction) In another skillet, combine the water, vinegar, onion, and peppercorns. Reduce the mixture by half, strain the liquid, and keep it at room temperature.

In a double boiler over low heat, add the egg yolks. Gradually incorporate half the reduction into the yolks, whisking until they become light and fluffy. Slowly add the butter to the yolks, whisking in a clockwise direction. Ensure the water in the double boiler is not too hot to prevent the eggs from cooking too quickly. If the sauce becomes too thick, add more of the reduction. Add all the butter; the yolks will stabilize the sauce without breaking.

Season the sauce with salt, pepper, lemon juice, and Worcestershire sauce to your taste. Add the crab meat or lobster meat, lightly warmed. Remove from heat and transfer to a plastic bowl. Keep it at room temperature.