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Potato Mayonnaise
Very small baked potato 1 teaspoon mustard 1 teaspoon salt 1 teaspoon powdered sugar 2 tablespoons vinegar 3/4 cup olive oil Remove and mash the inside of potato. Add mustard, salt, and powdered sugar; add one tablespoon vinegar, and rub mixture through a fine sieve. Add slowly oil and remaining vinegar. By the taste one would hardly realize eggs were not used in the making.
An eggless mayonnaise in which the starch and moisture of a baked potato do the emulsifying work of a yolk. It behaves like a real mayonnaise if the oil goes in slowly enough.
- The hinge: add the oil drop by dropThe hinge: add the oil slowly -- the recipe's only instruction on technique is "add slowly oil," and that is the whole trick. Let the oil in a little at a time at the start while you whisk hard; poured fast, the mixture can break into an oily slurry.
- Mustard means dry mustardMustard most likely means dry mustard -- a teaspoon of "mustard" in a dressing of this date is usually powdered mustard rather than a prepared paste from a jar. Prepared mustard would add vinegar and water and thin the base.
- Powdered sugarIn books of this period this usually meant finely granulated sugar rather than modern confectioners' sugar. Either will serve; dissolving it in the vinegar first avoids grittiness in a cold sauce.
- A very small potatoAim for something around 3 to 4 ounces, baked until fully soft. The flesh should be dry and mealy, so bake rather than boil, and use a floury potato such as russet.
- Work it warm, finish it coolSieve the potato while it is still warm, when it presses through easily and stays smooth, then let the paste come down towards room temperature before the oil goes in.
- Salt is on the high sideA full teaspoon of salt for about a cup of dressing reads as salty to modern palates. Add half, then taste at the end.
- Yield and keepingYou will get a little over a cup, enough for a salad for four to six. It thickens noticeably in the refrigerator and is best within two or three days, as cooked potato is a friendly medium for bacteria once the oil is emulsified through it.
- If it separatesStart again with a fresh spoonful of sieved potato and a little vinegar, then beat the broken sauce into it slowly, exactly as you would rescue a curdled egg mayonnaise.
Eggless mayonnaise turns up repeatedly in Anglo-American cookery books of the late nineteenth and early twentieth centuries, when eggs were expensive and seasonally scarce. Cooked potato is one of the substitutes recorded: its swollen starch helps hold oil in suspension, and it contributes almost no flavour of its own -- "By the taste one would hardly realize eggs were not used." The idea was not new to the period; potato and bread have long been used to carry oil in Mediterranean sauces such as skordalia and some versions of aioli.