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Mustard Sauce
To one tablespoonful of evaporated milk, add a teaspoonful of mustard, mix well and then beat in eight tablespoonfuls of olive oil, drop by drop, and one tablespoonful of vinegar.
This is a mayonnaise built on evaporated milk instead of egg yolk — the milk proteins do the emulsifying. It works, but only if the oil goes in slowly at the start.
- The hinge: add the oil slowlyOne tablespoon of milk is a very small amount of liquid to carry eight tablespoons of oil. The first two tablespoons of oil genuinely need to go in drop by drop, whisking constantly; after that you can move to a thin stream. Rush it and you get an oily split mess rather than a thick sauce.
- Which mustardThe book gives no clue. A teaspoon of dry mustard powder makes a sharp, thick sauce; a teaspoon of prepared mustard (a Dijon-style paste) makes a milder one and also adds emulsifying help. Either works.
- Evaporated milk, not condensedEvaporated milk is unsweetened concentrated milk. Sweetened condensed milk is a different product entirely and will ruin the sauce. Use it straight from the can, undiluted.
- Vinegar goes in lastThe recipe puts the acid in at the end; adding it earlier thins the base and can make the emulsion harder to start. Plain white or cider vinegar is in keeping; a teaspoon of lemon juice can stand in for part of it.
- SeasoningNo salt or pepper is specified, and the sauce needs both. Add about a quarter teaspoon of salt and a few grinds of pepper at the end, then taste — mustard sharpness reads differently once the oil is in.
- Yield and servingAbout two-thirds of a cup, enough for four to six people alongside cold beef, ham, tongue or chicken. Thin it with a teaspoon of milk if you want something closer to a dressing.
- If it breaksStart again in a clean bowl with a fresh tablespoon of evaporated milk and beat the split mixture into it drop by drop, exactly as you would rescue a broken mayonnaise.
- KeepingBecause it is dairy-based with no egg, treat it as a fresh sauce: refrigerate and use within two or three days. It will thicken in the cold and can be loosened with a little milk.
Eggless mayonnaise built on evaporated milk was a familiar trick of the interwar and wartime decades, when canned milk was a pantry staple in households without reliable refrigeration and eggs were periodically scarce. The chemistry is sound — milk proteins and the mucilage in mustard both help stabilise an oil-in-water emulsion — and milk-based mayonnaise of this kind is still made in parts of Latin America. Its place among cold-meat sauces reflects a period habit that has largely faded: the cold joint, sliced from Sunday's roast and served through the week, wanted a sharp dressing, and mustard was a usual answer. A sauce like this one had the added advantage of requiring no cooking at all.