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Potato Salad Dressing
Two eggs, butter size of egg, 1 teaspoon mustard, 1 tablespoon cornstarch or Five Roses flour, 2 cups water, 1 cup vinegar.
When cold, add sour cream. Let cool before adding the eggs.
A boiled dressing of the sort that preceded mayonnaise in most North American kitchens: vinegar and water thickened with starch and egg, softened with butter and cream. The instructions are compressed to the point of contradiction, so the order of work matters more than anything else here.
- Sort out the order firstRead the last sentence before you start. Heat the water, vinegar, butter, mustard and starch until thickened, let it cool to warm, then whisk in the beaten eggs and return it to gentle heat until it thickens again. The sour cream goes in only once the dressing is fully cold.
- Do not let the eggs go in hotThat is what the closing line is guarding against. Eggs dropped into boiling vinegar curdle instantly and no amount of beating brings them back.
- Bring the egg mixture to temperatureBecause the eggs are added off the boil, they can easily be left underdone. Hold the dressing over low heat or a water bath until it reaches 160F and coats a spoon; it will not thicken properly below that in any case.
- Butter size of eggAbout 2 oz, or 4 tablespoons. Nineteenth and early twentieth century cookbooks measured butter by comparison to eggs, walnuts and hazelnuts rather than by weight.
- MustardAlmost certainly dry mustard powder rather than prepared mustard from a jar, though the recipe does not say. If using powder, whisk it into the starch while everything is still dry or it will go lumpy.
- The thickening is light on purposeOne tablespoon of starch to three cups of liquid gives a pourable dressing, not a spoonable one. If you want something closer to modern potato salad dressing, the cream is where the body comes from, so use a generous half cup or more.
- Vinegar strengthOne part vinegar to two parts water assumes a household vinegar of ordinary strength. Standard 5 percent white or cider vinegar works as written; anything labelled double strength should be cut further.
- Yield and useThe liquid alone is three cups, so the finished dressing comes to something nearer four; enough for a large bowl of salad. Dress the potatoes while they are still warm so they absorb the dressing, then chill. Best used within a couple of days refrigerated.
Cooked or "boiled" dressings like this one were the everyday salad dressing of Canadian and American households well into the twentieth century, cheaper and more stable than an oil emulsion and far less likely to break in an unrefrigerated kitchen. Vinegar and mustard did the seasoning, flour or cornstarch did the work that oil does in mayonnaise, and sour cream stirred in at the end supplied the richness. The Five Roses Cook Book was published by the Lake of the Woods Milling Company to promote its Five Roses flour, and was assembled largely from recipes sent in by Canadian housewives, which explains both the brand plug in the ingredient list ("cornstarch or Five Roses flour") and the telegraphic style: these were notes written by cooks for other cooks who already knew what a boiled dressing was supposed to do.