Whisk all ingredients together in a stainless or enameled saucepan. When well blended, whisk over low heat until mixture is thick, foamy and warm to your finger. Do not bring too near to simmer or the eggs will scramble, but you must have enough heat to do the job. A wisp of steam rising over the surface usually indicates the sauce is done, after 2 to 4 minutes of whisking.
Serve within 20 to 30 minutes.
Note: With a longer wait, the sauce will usually separate but can be re-homogenized by beating again over heat. It will not be a foamy sauce, however, if reheated, it will usually be a smooth yellow cream, like a custard sauce.
Sabayon Sauce can be made in a double boiler over simmering water.