How To Caramelize Onions

Few things will skyrocket the flavor of your dish quite like caramelized onions. These tender, candy-sweet — yet savory! — morsels turn anything from a burger to a bowl of pasta into something instantly, deliciously gourmet. Accept no imitations: Caramelizing onions at home is easy to do. You just need a few onions, a pat of butter or some olive oil, a pan, and some time.

Any onion will caramelize, so don’t be shy about experimenting. Yellow and sweet onions, like Vidalia and Walla Walla, caramelize the most readily and are the most versatile in dishes. Red onions are fun for their deep purple color and are great on pizzas and salads. I rarely cook with white onions, but I imagine they’ll caramelize just like the rest! 

It’s best to caramelize three or four big onions at once in a process that takes about an hour. You can shave off some time by cooking just one or two onions, but I figure the more the merrier; if I have the time, I might as well make enough to last for a while. 

We compared six wildly different methods for caramelizing onions, from a quick 15-minute method to a long and low slow cooker technique. In the end, we found that you can’t rush true caramelized onions. Bump up the heat and they scorch; add brown sugar or balsamic too early, and they may look like caramelized onions, but they’ll lack that deeply caramelized, hauntingly savory flavor. 

Nope, the only way is to grab your biggest pan, set a burner to medium heat, and let those pungent alliums cook slowly. At this temperature, the sugars trapped inside the onion layers caramelize steadily, never burning but growing ever more golden and delicious.

Don’t feel that you have to hover by the stove. Once the onions are going, check on them every five or 10 minutes to give them a stir and see how things are coming along. Scrape up the sticky “fond” that builds up on the bottom of the pan and stir it into the onions. Adjust the heat as necessary to keep them cooking at a steady pace, but avoid burning. Let your nose and your tastebuds be your judge — when you can’t resist eating them straight out of the pan, they’re done.

It can take up to an hour to caramelize the onions, and if anyone tells you differently they’re lying.

Stainless steel or cast iron skillets are ideal for caramelizing onions. While you technically can caramelize onions in a nonstick skillet, part of what makes these onions so special is the fond that builds up on the bottom of the pan — scraping this up and stirring it into the onions gives them an even richer flavor — and this fond won’t form in a nonstick skillet.

Let’s talk about that fond! As the onions cook and release steam, some of their sugars get transferred to the bottom of the pan. It looks like the pot is burning, but don’t worry, it’s not! This sticky glaze quickly dissolves with a little liquid. At the beginning of cooking, the steam from the onions as you stir is enough to scrape up the fond. Then, as the onions dry and caramelize, deglaze the pan with water, broth, wine, or balsamic vinegar. 

So you’ve made caramelized onions — now what? Pile a spoonful of caramelized onions on baguette slices for a quick appetizer. You can also stir a scoop into soups, stir-fries, casseroles, pasta sauces, or braised dishes. They can go on top of pizza, layered onto burgers and sandwiches, or added to salads. I have trouble thinking of any dish that couldn’t use some caramelized onions! 

Store caramelized onions in the fridge for around a week, but they also freeze beautifully. Freeze them in little portion-sized patties or in tablespoon-sized portions (an ice cube tray works well for this!) so you can grab what you need for a sauce or a sandwich topping when you need it.

In September 2019, we pitted six of the most popular caramelized onion methods against one another to determine the best. The winner was a technique heralded by America’s Test Kitchen, which begins by steaming the onions, covered, over high heat. The onions are then cooked uncovered over medium-high heat until caramelized, at which point a baking soda solution is stirred in.

Given this newfound method, we felt it was time to look at our own caramelized onion technique to see how it stacked up. I got out my sharpest chef’s knife, slid onion goggles over my eyes, and started slicing.

Despite attending to both the timing and doneness indicators, the onions made using America’s Test Kitchen’s method burned, imparting a bitter taste. Ultimately, we found that Kitchn’s technique of cooking the sliced onions over moderate heat gave more consistent results. 

As a result of this testing, we did decide to clarify some steps. Toward the end of cooking as moisture from the onions evaporates, the onion’s sugars caramelize more quickly. We’ve added instructions to increase the frequency of stirring as the onions brown and form fond on the bottom of the pan. As a nod to the winning skills battle contender, we’ve also added the optional step to stir in a bit of baking soda in the end to intensify the color and sweetness of the onions.

— Patty, June 2020

• How To Make Caramelized Onions in the Slow Cooker
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