Soubise (French Onion Sauce)

It's a rare day that I say to myself, I know, I'm going to pick a very specific dish, go shopping for it, and then cook it for dinner. That requires more planning, shopping, and cooking time than I have on most weeknights. More often, I stare into my fridge, scour my pantry, and think, what the heck can I whip up that uses some of this stuff up and still tastes really good?

It's tremendous fun, and a rewarding process, to cook methodically through classic recipes. But everyday improvisational cooking is just as important as pulling off a special-occasion dish. The key, aside from some creativity and good instincts, is to have a library of tricks up your sleeve—techniques and recipes that you keep in the back of your mind and can riff on in a pinch. Here's one: soubise sauce.

I thought of it a few days ago when I bought a few too many onions for my tarte flambée recipe, and was trying to come up with of a good way to use them. Soubise, an old-school French sauce made mostly from onions, isn't all too common these days, but it should be. It's incredibly easy to prepare, works with all sorts of meats—from roast chicken to pork and even fish—and lends itself nicely to variation.

The original recipe, going back to at least Escoffier, calls for cooking onions in butter until very soft but not at all browned, then adding bechamel to the pot and simmering them together before finally puréeing them into a smooth, thick sauce. (There's also a variation with rice in place of the bechamel, though even Escoffier recommends against it.) Since then, the sauce has changed a bit, most often lightened, if you can call it that, with cream in place of the bechamel.

I'd never made the bechamel version before, so I whipped one up just to see what it was like, and indeed it tastes heavier and starchy compared to plain cream. I think the modern cream-based version is the way to go.

Some recipes also say to blanch the onions in salted water before sautéing for a more refined onion flavor, so I tried that out as well. It's interesting to note how the blanched onions stayed more white throughout sautéing than the non-blanched ones did; presumably the natural sugars on the cut surface of the onion are washed off in the water, leading to almost no caramelization at all.

Tasting them side by side, I preferred the more pronounced, sweeter flavor of the non-blanched onions—that subtle caramelization has its benefits.

A plain soubise, seasoned with salt, pepper, and maybe a dash of grated nutmeg, is tasty enough, but it's still something of a blank canvas that's just begging for other flavors. For this recipe, I whisked in curry powder, which plays off the onion and cream well, then paired it with a basic roast chicken. It's an impressively elegant dish for something that's fundamentally so simple; a creamy, oniony gravy that feels more luxurious than a pan sauce.

The sauce is so easy you can whip it up while the chicken is in the oven and have dinner on the table in about an hour. The only real trick is making sure that the onions soften without browning—a heavy saucepan preferably with an aluminum core for better heat distribution is the best tool for the job, though a thinner pan set on a heat diffuser or within a larger skillet would do the trick as well.

The best part is that it's open to all sorts of variation. You could substitute some of the cream with stock for an even lighter and more flavorful sauce, or play with other flavorings. Whisking some grated cheese, like Gruyere, into the sauce right before serving would be amazing too, almost like a mashup of soubise and mornay (a cheesy bechamel sauce).

The possibilities are endless. All you need to start are a few extra onions.