Have you ever heard of fond? According to Food Network, the word comes from the French for “base,” and refers to the browned bits of food that remain stuck to the bottom of the pan after you’ve browned meat or vegetables. Full of concentrated flavor, the fond makes an excellent base for a pan sauce – as long as you add some liquid to “deglaze” the pan and loosen the fond from the bottom.
In the case of onions, plenty of fond adheres to the pan during the process of caramelizing, and the substance is full of richness and sweetness from the long-cooked onions. Kitchn advises never letting the fond go to waste. Instead, you should always deglaze the pan at the end of the cooking process, right before seasoning and serving the onions. The outlet advises adding a bit of wine, broth, or vinegar to the cooked onions. Water will do in a pinch but doesn’t impart any extra flavor. Also use a spoon to scrape the fond from the pan and reincorporate it into the onions. When reunited with this flavorful substance, your caramelized onions will be the rich, sweet, jammy ones that are the stuff of dreams.