Soubise Sauce

A classic onion purée sauce built on a velouté base. The double blanching is the whole point: it strips the onions of sulphurous sharpness so the finished sauce tastes sweet and mild rather than raw.

• Do not skip the second waterFive minutes in boiling water, drained, then fresh boiling water until fully soft. Cooking the onions in a single pot of water leaves the sauce with a harsh, oniony edge that cream will not hide.
• Velouté, in briefVelouté is a white roux — equal butter and flour cooked without colouring — loosened with a light stock: veal, chicken, or fish, chosen to match what the sauce will accompany. For mutton or pork chops, a chicken or veal stock is the usual choice.
• Sieve or blenderRubbing soft onions through a sieve with a wooden spoon or the back of a ladle gives the silkiest result. A food processor or immersion blender works, though it traps more air and gives a paler, frothier purée; pass it through a fine strainer afterward if you want the classic texture.
• Onion quantityTwo cups sliced is roughly two medium yellow onions, about 8 oz. Cooked and sieved they reduce to well under a cup of purée.
• ConsistencyAdding a cup of velouté plus half a cup of cream to the purée gives a pourable sauce. If it thins too much, simmer gently to reduce rather than adding more flour, which dulls the onion flavour.
• HeatOnce the cream is in, keep the pan below a simmer. A cream-enriched velouté will break or catch on the bottom if boiled hard.
• YieldAbout two cups, enough for four to six servings alongside chops or eggs.
• SeasoningSweet onion purée wants more salt than you expect, and white pepper rather than black if you care about appearance. Some French versions add a grating of nutmeg, though this recipe calls only for salt and pepper.