Sour Cream Dressing

A three-ingredient dressing that depends entirely on the cream: what the book calls "rich sour cream" was cultured heavy cream, thick enough to hold air when beaten.

• The cream is the recipeUse full-fat cultured sour cream or creme fraiche, not light or reduced-fat, which will slacken and weep rather than thicken. Creme fraiche whips more reliably than commercial sour cream, which is often stabilised with gums.
• Why five minutesThe beating is aerating, not emulsifying. The goal is a dressing light enough to sit on cucumber slices instead of pooling under them; stop once it has thickened and holds its shape, and do not carry on past that, since a very rich cream can eventually churn.
• Keep everything cold"Very cold" is not decorative. Chill the bowl and beaters, and work quickly; cream above about 45F whips poorly and will not hold.
• Lemon juice is a seasoning, not an acidulantHalf a teaspoon in a cup is barely a brightener. The recipe has it going in as you beat, and at that quantity, into cream that is already acidic, it does no harm to the texture.
• Powdered sugarModern confectioners' sugar contains cornstarch, which is harmless here and slightly helps the body. One tablespoon gives a faintly sweet dressing typical of period cucumber salads; halve it if that reads as dessert-like to you.
• SaltNone is called for and none is needed if the cucumbers are salted. If you skip salting the cucumbers, a pinch in the dressing keeps it from tasting flat.
• Yield and timingA little over a cup once aerated, enough to dress a couple of cucumbers. Dress at the table; sliced cucumber releases water quickly once dressed and the dressing thins.