The soubise sauce is a classic cream sauce for vegetables made by sautéeing onions and adding them to a basic béchamel sauce. It's an excellent accompaniment for vegetables, eggs or chicken, or as a base for making casseroles. Traditionally the onions were puréed before adding, but this isn't essential. But if you don't purée them, you'll want to chop them pretty small.
The word soubise originally referred to a garnish or condiment (it is probably overstating it to call it a side dish) made of slow-cooked rice and onions, along with cream and Gruyere or Ementhaller cheese. There was a restaurant in L.A. some years ago that served it with roast meats, and it was rather nice. Note that the rice was not puréed. It was a sort of creamy, oniony porridge.
If I recall correctly, it was an arborio rice, which is the same rice used for making risotto. Arborio rice is a very starchy rice, and if you've made risotto, you know how the starch cooking out of the rice gives the risotto a cream quality. And that's just what it does in the soubise as well.
To understand the soubise sauce, then, it helps to see it as a reinterpretation of the condiment soubise as a sauce, rather than as a variation on béchamel that includes onions. (Though in effect, that's what it is — at least in this recipe.)
One of the most simple variations on the classic soubise sauce, add some tomato purée to the sauce just before serving (see below).
I've discussed this elsewhere, but caramelizing onions takes time. Plan on taking half an hour to do it. If you try to rush it, you will get toasted onions, or browned onions, or grilled onions, or possibly burnt onions. Any of these (except the last one) will be fine. But they won't be as flavorful as truly caramelized onions. I wish I could speed up time for you. But caramelized onions are one kitchen task for which there is no real shortcut. My best suggestion to you is to listen to an audiobook or podcast or something while they're caramelizing. Here's a tutorial on how to caramelize onions.
- 1 lb onions, chopped
- 4 Tbsp butter
- 1 quart béchamel sauce
- 2 cups tomato purée (optional)
- In a heavy-bottomed saucepan, melt the butter and cook the onions until soft and translucent, but don't let them turn brown.
- Transfer cooked onions to a food processor. Purée briefly and then return them to the pot.
- Whisk the béchamel into the puréed onions and bring the sauce to a simmer.
- Add optional tomato purée and serve right away.