Fold the caviar into the sauce hollandaise just before serving with delicately poached fish.
Put the white wine, vinegar, chopped shallots and a little ground black pepper in a small pan and reduce it by fast boiling to about 2 Tbsp. Strain it and add a few drops of cold water. Put this essence in the top half of a double saucepan or in a bowl which will fit into the top of an ordinary saucepan. This underneath saucepan should be half full of warm water and put on to a gentle flame.
To the liquid already in the top pan, add half the butter, cut into small pieces. Let it melt quickly, then add the rest, stirring all the time. Now add, gradually, the beaten yolks of the eggs and stir very carefully until the sauce thickens. Add salt if necessary, which will depend on whether the butter used is salted or unsalted, and a few drops of lemon juice and a few of cold water. Take the sauce from the fire and stir in the chopped tarragon, and the sauce is ready. At no time should the water underneath the sauce boil and the sauce is not intended to be served hot, but tepid.
Mint instead of tarragon turns béarnaise into paloise, a modern variation, useful for serving with lamb and mutton.
If you should be obliged to make your béarnaise in advance the least risky way of reheating it is to put the bowl which contains it inside another one containing hot water and stir it for a few seconds, but not over a flame. Never mind if the sauce is not very hot; it is better to have it cool than curdled.
A classic of Genoa, Italy, this sauce has many variations. Add more or less garlic to suit your taste. If the basil tastes too strong for you, replace part of it with parsley. If you have any left over, put it in a small glass or plastic container, smooth its surface, and pour a thin film of olive oil on top to cover; then cover the container with a lid or plastic wrap and refrigerate for 3 to 5 days. Stir in the oil before use.
Put all the ingredients in a food processor fitted with the metal blade. Pulse the machine on and off to chop them coarsely, then scrape down the bowl. Process continuously, stopping once or twice to scrape down the bowl, until the pesto is smooth.
Yield: makes about 1 cup