Vinegar Sauce with Shallots and Mustard

A working vinaigrette from Ranhofer's cold sauce chapter, given in gills and with the mustard left to the cook's judgment. The proportions are sound; only the vocabulary needs updating.

• GillsA gill is half a cup. One gill of vinegar and two gills of oil means 1/2 cup vinegar to 1 cup oil — the standard one-to-two ratio, which still holds. Total yield is about 1 1/2 cups, enough for several salads or a large platter of cold meat.
• Sweet oilNineteenth-century American and English kitchens used "sweet oil" to mean olive oil. Use a decent but not aggressively peppery olive oil; a very assertive oil will fight the shallot.
• The blanching is the pointDropping the diced shallot into boiling water for thirty seconds and draining it strips out the raw sulfurous bite and stops the sauce turning harsh as it sits. Skip this and you have an ordinary shallot vinaigrette that grows sharper by the hour.
• Cut sizeOne-eighth inch dice is small and deliberate — it suspends in the sauce and spoons out evenly rather than sinking. Ranhofer means it; a rough mince gives a different sauce.
• "Some mustard"Genuinely unspecified. Start with a teaspoon of smooth Dijon-style prepared mustard, which also helps hold the emulsion, and adjust.
• VinegarWhite wine vinegar suits this style, though the recipe does not say. Vinegar strength was not standardised in the period, so taste before adding all of it if you are using something sharp.
• AssemblySalt the vinegar first, as written — salt dissolves in the vinegar and not in the oil. Then whisk in the oil, the mustard, and the shallots. The sauce will separate on standing; whisk again before serving.