In the top of a double boiler, combine shallots and vinegar; simmer over hot water, stirring occasionally, until until nearly all of the vinegar has been absorbed. Stir in 3 egg yolks, 1/4 teaspoon of sea salt, 1/4 teaspoon of freshly ground black pepper and a tablespoon of butter.

Cook over the hot water in the double boiler, adding butter gradually in small pieces, until 1/2 cup of butter has been used. Stir in parsley.

The sauce should have the same consistency as mayonnaise. It can be used hot or cold over broiled steak, lamb or pork chops or even fish.