A step-by-step guide for perfect caramelized onions, every time.

By Mary-Frances Heck
Updated January 06, 2020
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Sweet and umami-packed, caramelized onions make dishes of all kinds better. Sad soup? Give your mirepoix a boost by caramelizing the onions before adding the other ingredients. Casserole lacks oomph, and you dare not rely on that can of cream-of-something soup? Caramelized onions are here for you. Have an onion and dried pasta on hand? Caramelize that onion, and toss with cooked pasta, maybe an herb or some pepper and cheese, and boom—dinner is served.

The only catch to this pantry powerhouse is that caramelized onions take over an hour to cook properly, and chances are high they will scorch a little and turn acrid and bitter. When I was in culinary school, I was taught that the enemies of caramelization are movement and moisture. I have come to respectfully disagree, at least where onions are concerned. Those elements are, in fact, exactly what’s needed to achieve caramelized onion nirvana.

Enter this fail-safe technique for caramelizing onions, which uses a lid and some water to manipulate the moisture of the cooking onions, guaranteeing sublime sweetness. Properly caramelized onions are spreadably soft but maintain their individual strands, are uniform in their mahogany color, and taste silky-sweet with a hint of onion bite. They cook down to a third of their original volume, giving up the majority of their moisture while their sugars slowly caramelize, darkening into a slump of flavor fit for improving any number of wintertime dishes.

Even cooking starts with even cutting. It’s more important that the onions be cut uniformly than cut a specific size. If it’s easier for you to cut onions into 1/2-inch pieces rather than 1/4-inch pieces, no problem. Just be consistent—the onions will still caramelize evenly, though larger cuts may take a bit longer to cook.

Victor Protasio

Also key: stirring the onions and scraping down the sides of the pan often to ensure no strand darkens faster than another. A heatproof rubber spatula is the tool for this job; it’s stiff enough to scrape the bottom of the pan but flexible enough to clean the sides.

Since they take a bit of time and a careful eye, I do the bulk of my onion caramelizing on the weekend. I let the cooked onions cool to room temperature then divide them into ice cube trays to freeze and use throughout the week. Sometimes, depending on what I plan to use them for, I puree them before freezing them. The pureed onion ice cubes are great for melting into sauces and soups, while longer onion strands are ideal for adding to rustic soups and clinging to curly pasta shapes.

However you plan to use these caramelized onions, start with more onions than you think you’ll need. They’ll cook down to a fraction of their original volume.

Victor Protasio

Caramelized Onions, Step By Step

Be sure to choose a heavy-bottomed skillet with a light interior—it will make it easier to monitor the browned bits in the bottom of the pan to avoid scorching the onions. For the full recipe, go here.

1. Slice Onions

Peel the onions. Halve and slice lengthwise into uniform pieces (about 3/8-inch-wide slices are ideal, but a little larger or smaller is fine).

2. Heat Oil

Heat oil in a 10- to 12-inch high-sided skillet over medium-high. Add half the onions; turn to coat. Cook until sizzling, about 2 minutes. Add remaining onions in handfuls, folding with tongs to coat in oil. (Pan will be very full at this point).

3. Cook Onions

Cook onions, tossing often with tongs, until hot and sizzling, about 3 minutes. Add salt (to help draw moisture out of the onions), and toss to combine.

4. Cover

Cover, reduce heat to medium, and cook until onions have collapsed to half their height and a pool of liquid has collected in bottom of skillet, about 10 minutes.

5. Fold

Fold onions with a spatula, scraping bottom of pan to ensure they don’t stick or scorch. Cook, stirring every 5 to 6 minutes and reducing heat as necessary to maintain a gentle simmer, until liquid has evaporated, about 35 minutes.

6. Scrape

When pan looks dry, increase heat to medium, and scrape bottom and sides of pan with a rubber spatula, shaping mound of onions into an even patty pulled away from edges of pan. This careful shaping will help the onions cook evenly and prevent scorched bits around the edges.

7. Deglaze

If onions start to stick to bottom of pan, or if fond on bottom of pan darkens more quickly than the onions, add a splash of water, and stir and scrape to loosen any browned bits. Stir onions well until they are uniform in color, and reshape into a patty.

8. Finish

Continue cooking, stirring, splashing in additional water, and reshaping into a patty as needed, until onions are the color of bourbon, 35 to 45 minutes. Remove onions from pan, and use as desired.

3 Ways to Use Caramelized Onions

Quick Quiches

Spread 1 cup caramelized onions in the bottom of a parbaked 9-inch tart shell; top with 1 cup diced ham and 6 eggs beaten with 1 cup heavy cream. Bake at 350°F about 35 minutes.

Pasta Pronto

Toss 1 pound cooked short pasta (such as casarecce or penne) with 1 cup caramelized onions, 1/2 cup pasta cooking liquid, grated parmesan, and black pepper.

Soup Saver

Stir 1/4 cup pureed caramelized onions into brothy vegetable soups to thicken them slightly and add an extra layer of savory flavor. They’re also great in mashed potatoes.