This condiment is the flavorful reduction of slow-cooked onions with herbs and balsamic vinegar. Yes, it takes time and patience, but the result is a thick, sweet-savory-tangy sauce with incredible depth of flavor that can be used in a multitude of ways. I love it on burgers, as a topping to goat cheese toast, a garnish for creamy soups, and an addition to grown-up grilled cheese sandwiches.
A large stockpot is essential; you’ll start with 8 cups of onions, which reduce to about 2 cups. Slice the onions thinly, whether by hand, with a mandolin, or in a food processor. Take the time to let the onions cook slowly, and have the patience to stir them often so they don’t burn.
I love adding a good-quality balsamic vinegar, which gives it a rich and dark flavor, but you can also try other types of vinegars, such as red wine, white balsamic, or champagne.
Makes about 2 cups
- 1/4 cup olive oil
- 1 tablespoon butter
- 6 to 8 large onions, thinly sliced
- 1 teaspoon fresh thyme leaves, stems removed
- 1 teaspoon fresh rosemary, chopped
- 1 teaspoon sea salt
- 1 teaspoon freshly ground black pepper
- 1/2 cup balsamic vinegar
In a large stockpot, add the olive oil and butter and melt over medium heat. Add the onions and stir to coat well. Lower the heat and cook, stirring once in a while, for about 60 minutes. The onions should be soft, glossy, and golden-colored.
Add the thyme and rosemary, season with salt and pepper, and add the balsamic vinegar. Cook for another 15 to 20 minutes, until all the juices have evaporated and the onions have turned into a thick sauce. Taste to adjust seasonings.
Use immediately, or let it cool to room temperature and store in lidded jars in the fridge for up to 2 weeks.