Tomato Tartare

A two-ingredient derivative sauce that assumes you already have tartare sauce on hand. Everything depends on what goes into that base and how wet the tomato element is.

• What tartare sauce meant hereIn a book of this vintage, tartare sauce is thick mayonnaise worked with chopped capers, gherkins or pickles, shallot or onion, and parsley, sometimes sharpened with a little tarragon vinegar. A commercial jarred tartare will work but is usually sweeter and thinner than the intended base.
• Catsup versus pulpPeriod tomato catsup was thinner, more vinegary and more heavily spiced with clove and allspice than modern ketchup, which is markedly sweeter. If you use ketchup the sauce will read as a sweet cocktail-style dressing; cooked tomato pulp gives the drier, more savoury result the recipe allows for.
• Cooked tomato pulpMost likely tomatoes stewed down and passed through a sieve to remove skin and seed, and reduced so the pulp is thick rather than watery; the recipe does not specify. Canned tomato passata reduced by about half is a near equivalent. Very watery pulp will slacken the mayonnaise.
• Add the tomato graduallyFold the tomato in a spoonful at a time rather than tipping it in at once. Three tablespoons into a cup and a half of emulsion is a modest addition that should hold, but adding it slowly and stirring gently rather than hard keeps the sauce from slackening.
• Season after, not beforeBoth catsup and reduced pulp bring their own salt, sugar and acid. Taste once the tomato is in and correct with lemon juice or a little vinegar; the sauce should stay sharp enough to cut fried shellfish.
• Yield and servingAbout 1 2/3 cups, enough for eight to ten servings alongside fried oysters, scallops or crab cakes. Rest it covered in the refrigerator for half an hour so the pickle and tomato marry, and serve it cold as directed.
• Raw egg in the baseIf you make the mayonnaise yourself the sauce contains uncooked egg yolk. Use pasteurized eggs if serving anyone elderly, pregnant or immune-compromised, keep it refrigerated, and use it within two or three days.