Soubise (sue-BEEZ) is a classic French white sauce that deserves a place in the contemporary American kitchen. Simple to make with common ingredients, soubise is defined by the onion, this one including both onion and shallot, blended into a béchamel sauce. Good hot or cold, the versatile sauce goes well with roasted or grilled/barbecued meats and with vegetables. Here I turn it into the backdrop for hearty macaroni and cheese, an excellent side dish or vegetarian main course. Escoffier blanched his onions before adding them to the béchamel, but I think the sauce benefits from the complexity of the caramelized onions. Either way, the sauce is great with grilled onions or with seared scallops or sautéed chicken. And it can replace the béchamel base in the classic cheese soufflé.