Preparation

• Finely chop the garlic on a cutting board. Sprinkle the salt over it and repeatedly scrape the flat side of the knife over the garlic to mash it to a paste. Scrape the garlic paste into a medium bowl. Add the mustard, vinegar, and water, and whisk until the salt is dissolved. Gradually whisk in the oil in a thin stream: the sauce should thicken slightly.
• Whisk in the onion, capers, pickles, tomato, parsley, and egg (if using). Taste and correct the seasonings, adding salt and pepper to taste. Serve within a few hours of making and whisk well before serving.

This vinaigrette has enough substance to stand up to grilled poultry or beef, but it especially complements seafood. Spoon a generous portion over a grilled halibut or swordfish steak. If you have any left over, toss it with boiled potatoes for a quick potato salad.