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 …