Onion Sauce

A plain white onion sauce of the type served with boiled mutton or fowl. The whole thing takes about twenty-five minutes, and the only real decision is how smooth you want it.

• Butter "half the size of an egg"Conventionally read as about 2 tablespoons, or roughly 1 ounce of butter. This is a common nineteenth-century measure, and like all such measures it is an approximation rather than an exact quantity.
• Half pint milkOne cup in American measure. Whole milk gives the body the recipe assumes; skim will need slightly more flour.
• White onionsThree or four medium onions cook down to a couple of cups or so of minced onion, which is a great deal of onion for a cup of milk. The sauce is meant to be thick and chunky rather than a thin, smooth sauce. Use two if you want something closer to a modern cream sauce.
• Boil till tenderPeel, halve, and simmer in salted water 15 to 20 minutes until a knife passes through with no resistance. Undercooked onion stays sharp and grainy and no amount of milk will hide it. Drain well or the sauce turns watery.
• The flour slurryWhisk the tablespoon of flour into 2 to 3 tablespoons of cold milk until smooth before it goes anywhere near the pan, then stir it into the simmering milk and cook two or three minutes to lose the raw taste. Added dry it will lump instantly.
• Keep the heat lowMilk on direct heat scorches on the bottom of the pan and the sauce picks up a burnt note that reads as bitter. A heavy saucepan and a moderate flame, stirring often.
• Yield and servingAround two cups, enough for four. It belongs with boiled or roast mutton, boiled fowl, tripe, or rabbit. A grating of nutmeg would not be out of place for the period if you want it.
• If you want it smoothPuree the cooked onions in a blender or press them through a sieve before adding. Some period cookbooks do call for rubbing the onions through a sieve for a smoother sauce.