A road trip Mary Ellen Carroll took with her grandfather inspired this sweet red-onion condiment. You'll know the onions are done when they are very tender and their juices are syrupy. Don't overcook the onions or the sweetness will be cloying. Carroll slathers any leftovers on slices of buttered baguette. More Condiments
How to Make It
Step
In a medium saucepan, melt the butter in the olive oil. Add the onions and cook over moderate heat until softened, about 7 minutes. Add the water, balsamic vinegar, sugar and rosemary and season with salt. Cover partially and simmer over low heat until tender, about 30 minutes. Uncover the onions and simmer until the juices are syrupy, about 15 minutes longer. Discard the rosemary and serve warm.
Make Ahead
The onions can be refrigerated overnight. Reheat gently.