What it means
The overnight popularity of virtuous vegetables such as cauliflower might have something to do with chefs' willingness to slather them in soubise, a bechamel sauce offshoot that's padded with onions.
When soubise originated in 18th-century France, it was often thickened with rice. In his seminal 1903 cookbook, Auguste Escoffier suggested adding "one-quarter lb. of Carolina rice" to onions stewed in bacon fat, white consomme, powdered sugar and salt. But he added that the mixture of bechamel in soubise "is preferable to that of rice, seeing that it makes it smoother."
Many modern soubise recipes call for combining sauteed onions with bechamel, or white sauce, the simplest of the five "mother sauces" considered the building blocks of classical cuisine. As culinary students learn in their first few classes, bechamel is made by cooking flour and butter in milk.
Where we saw it
Two Boroughs Larder (Roasted Brussels sprouts, soubise, salumi vinaigrette, $8)
Where else you can try it
Soubise is a standard element of any classically trained chef's repertoire: It's surfaced at FIG, Old Village Post House and The Macintosh, among other local restaurants.
Where to buy it
Even in France, you can't find powdered soubise mix (nor, really, would you want to.) But if you're adept with a whisk, it's not hard to make soubise at home: The sauce works over meat and pasta as well as vegetables.