How to caramelize onions in a skillet or oven

• Caramelizing onions slowly in butter or oil produces sweet, delicious results.
• You can caramelize onions in a large skillet or in the oven.
• Spanish and Vidalia onions are best for caramelizing.
• Visit Insider's Home & Kitchen Reference library for more stories.

Hardly any ingredient amps up the flavor of a recipe like caramelized onions. Savory yet sweet, with a texture that melts in your mouth, they instantly elevate any dish, whether a gourmet pasta or a crowd-pleasing dip. Best of all, only three ingredients are needed to make them.

What makes caramelized onions so special? As the onions cook down over a long period of time, their natural sugars get released and broken down. According to Herve Malivert, Director of Culinary Affairs at the Institute of Culinary Education, the resulting sweet and subtly tangy flavor can help to cut through the fat in many rich dishes, like burgers, steaks, and pizzas.

The most important thing to remember when caramelizing onions is that perfection requires patience: if you try to rush the process, you'll compromise the texture and flavor.

What's the best onion for caramelizing?

Any onion will caramelize, but yellow onions are ideal for all-purpose caramelizing. Spanish onions are typically used for caramelizing because they have a balanced sugar content, says Charbel Adaimy, Executive Chef at Messhall Kitchen. However, Vidalia and Maui onions can be used for an even sweeter result. Red onions also work but beware that they're slightly more pungent and less sweet in flavor.

How long does it take to caramelize onions?

If you're looking for a truly deep, rich, sweet flavor, you cannot rush caramelized onions.

Caramelized onions typically take 45 minutes to an hour. It's best to caramelize two to four large onions at once. If you have leftovers, they can be stored in the fridge for up to five days.

Caramelizing onions in the oven

The advantage to caramelizing onions in the oven is that they brown more slowly, meaning you can avoid standing over the stove and stirring them continuously. The disadvantage, says Adaimy, is that they take longer to caramelize this way, and the results can be slightly less consistent - with some pieces browner than others.

1. Preheat the oven to 350 degrees.

2. Slice the onions. Slice off the root and stem of each onion. Halve each onion vertically from root to stem, remove the skins, and thinly slice each half.

3. Toss the onions in fat. In a bowl, combine the onions with 1 teaspoon of salt and 2 tablespoons of oil and toss until well-coated.

4. Roast until soft and golden-brown. Place the onions on a baking sheet lined with parchment paper, season with salt, and roast it in the oven. Set a timer every 10-15 minutes to stir the onions so they don't burn and get evenly browned. This may take 45 minutes to an hour.

Troubleshooting caramelized onions

Although caramelizing onions is easy to do on the stove or in the oven, the process requires patience and care at the risk of potentially ruining the taste and texture.

• Burning or sticking to the pan: If this starts to happen, either lower the heat or transfer the non-burned pieces to a new pan, Adaimy recommends.
• Too much oil: The onions will get too greasy and may not brown as well while swimming in fat. To fix this, Malivert suggests removing onions from the pan, draining some of the oil out, and then transferring the onions back into the pan to continue cooking.
• Not enough fat: If there's too little butter or oil, the onions may start to steam instead of sautéeing, says Adaimy. Just add a tablespoon or so more oil or butter ASAP while the onions are still cooking.

What you can use caramelized onions for

Once the onions are perfectly golden-brown and soft, there are a variety of dishes to add them to.

• Grilled cheese: Adaimy says caramelized onions add a decadent jammy texture and earthy flavor that upgrades this classic comfort food. They can also be used in other sandwiches like roast beef, a BLT, or hummus and veggies.
• Soups: Traditional French onion soup recipes call for onions caramelized in butter. Caramelized onions can also enhance the flavor of chicken noodle soup.
• Steak: Any cut of steak can benefit from this salty-sweet garnish.
• Burgers: Caramelized onions are a popular topping for blue cheese burgers in particular.
• Pizza and flatbread: While they're versatile enough to complement a wide variety of pies, they really shine on white pizzas and flatbreads with salty meats like bacon and prosciutto, and earthy vegetables like mushrooms, spinach, and chard.

How to store caramelized onions

If you're making caramelized onions ahead of time, Adaimy says they can be stored for five days.

Make sure to let the onions cool after cooking before sealing them in an airtight container or plastic bag. Then place them in the refrigerator.

According to Malivert, caramelized onions can also be frozen for up to a month. Store them in a plastic bag - or, if you want them pre-portioned, pack them into an ice cube tray or muffin tin, pop them out when frozen, and then place those portions into a sealed container before leaving them in the freezer again.

Insider's takeaway

Caramelized onions can skyrocket the flavor of a wide range of dishes. If you want restaurant-worthy perfection, it's better to caramelize them the old-fashioned way on the stovetop. However, if you have a little extra time on your hands and don't want to babysit them, caramelizing onions in the oven is another option that frees you up to multitask while cooking. Whichever method you choose, remember not to rush the process, as achieving that deep flavor and color takes time.

Once the onions begin to brown, it's important to keep stirring them and scrape them from the bottom of the pan to prevent them from burning.

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