Put the egg yolks and the mustard in a bowl and whisk thoroughly together. Start adding the oil drop by drop at first, then in a stream as you keep beating with the whisk. When you have a very thick sauce, the consistency of sour cream or thicker, add the lemon, the balsamic vinegar and the salt and pepper. Beat again until smooth. Whisk in more oil if the sauce is too thin or runny.

This is excellent with boiled meats and poached or baked west coast salmon, or on paper thin slices of raw beef tenderloin, together with a good amount of extra virgin olive oil, salt and pepper and additional balsamic vinegar.