How to Caramelize Onions

Caramelized Onions are a sweet and savory staple which can be used in countless recipes for burgers, steaks, chicken, dip, and so much more! Thinly sliced onions are sautéed in oil and butter until golden-brown and rich in flavor. While not a quick fix, this easy and classic recipe is well worth the wait!

There are few things more addictive than a skillet of beautifully caramelized onions. 

Oftentimes, I find their sweet and savory flavor to be the PERFECT accompaniment to bring a recipe to the next level. Whether as a topping for a steak or a burger, mixed into a quiche, or even serving as the base to a rich French onion soup, they never disappoint.

While it can be tempting to try and quickly whip up caramelized onions, there’s simply no replacement for the rich depth of flavor that comes with a little time and patience.

By allowing pan-fried onions the time to fully release their natural sugars and to brown all the way through, you can be assured that their flavor will far surpass that of any shortcut. 

So while this isn’t a technique which can be done last minute, it is still a super easy way to add a rich, savory, buttery flavor to your favorite recipes!

Ingredients

One of the best things about this cooking technique is how few items it actually takes. The simple ingredients you need to make this caramelized onions recipe include:

• Onions. Sweet onions like Vidalias are the best type to caramelize, for their high natural sugar content. Any other variety will work too, but may need to be supplemented with a pinch of sugar to reach the desired sweetness level.
• Oil. Because of the relatively low temperature at which caramelization occurs, any type of oil may be used, regardless of smoke point. A more mildly flavored oil, like vegetable or avocado oil, is recommended in order to avoid overpowering the sweetness of the onions.
• Butter. A high-quality butter is added toward the end of cooking, to provide an extra layer of richness and flavor. This may be omitted or substituted with vegan butter for a dairy-free diet, or with ghee for a Paleo or Whole30 diet.

How to Make Caramelized Onions

The basic steps for making caramelized onions are as follows: 

Slice the Onions

The thinner the onions are sliced, the more quickly they will caramelize. For an ideal balance between cooking time and keeping the onions from falling apart as they cook, they should typically be sliced about ¼ inch thick.

For more information, learn how to cut an onion here.

After slicing, any individual layers of the onions still stuck together should be separated from each other. This enables them to have even contact with the skillet and the heat so they cook at similar rates.

Prep the Skillet

Heat the oil in a large stainless steel skillet over medium-low heat for several minutes, then add the onions. Stainless steel works best because it conducts heat more evenly than a non-stick skillet, and allows the onions to develop that beautiful browning over time. 

At this stage, a pinch of salt can be added, to taste. If done early, this will help to draw moisture out of the onions and allow them to brown more thoroughly, giving them more flavor in the process.

The onions should be sizzling, but not so hot that they immediately begin browning, otherwise they’ll burn before they have a chance to caramelize. If it looks like they’re starting to cook too fast, simply lower the heat, add a couple tablespoons of water, and scrape any browned bits off the bottom of the pan and into the onions. 

Cook Low and Slow

Cook the onions for 40-50 minutes, stirring occasionally. Once they have begun to soften, stir them every 3-5 minutes. This gives them enough time early on to kickstart the cooking process without burning later.

At the 30-minute mark, when the onions have turned a light yellow color, add the butter and stir to combine. This allows the onions to soak up that extra bit of fat and salt from the butter, amplifying their flavor without giving the butter time to burn.

Continue cooking as directed until they have reached a deep golden brown and the ideal sweet, savory taste. Monitor them closely at this point, as they could burn easily.

A small pinch of salt or sugar may also be used here, to further highlight the sweet and savory flavors, to taste.

Meal Prep and Storage

• To Prep-Ahead: Onions can be pre-sliced and stored in an airtight container in the fridge for up to 3-5 days. 
• To Store: Leftovers may be stored in an airtight container in the fridge for up to 3-5 days.
• To Freeze: Leftovers may be stored in a freezer-safe container or freezer bag for up to 3 months. An ice cube tray or muffin tin can also be used to make individual portions before freezing.
• To Reheat: When frozen it is recommended to put the onions in the fridge to thaw at least an hour ahead of use. Once thawed, the onions can be reheated over low heat in a skillet, or in the microwave for 30 seconds at a time until warmed through.

Dietary Modifications

The recipe you’ll find below is already gluten-free, vegetarian, keto, Paleo, and Whole30 as written. Here are some adjustments and substitutions you can make to help it fit your other dietary requirements:

• Dairy-Free/Vegan: Omit the butter, or replace it with a vegan butter alternative. 
• Reduced Sodium: Use an unsalted butter, and/or omit the salt entirely.

FAQs

Expert Tips and Tricks

• Select steel. A large stainless steel skillet is the ideal tool for caramelizing onions, because they conduct heat the best and help food brown easier than a non-stick pan.
• Give them room. Use a big enough pan that the onions aren’t crowded before they’ve started shrinking down, to ensure they all cook at the same rate.
• Use more than butter. While butter adds a lot of amazing flavor to caramelized onions, it tends to burn, so a normal cooking oil should be used for the initial cooking process.
• Quicker caramelization. A pinch of baking soda added to the onions can help them caramelize faster by encouraging browning, but remember that doing so will break them down and give them an almost jam-like consistency.
• Remember to deglaze. There’s TONS of flavor packed into the brown bits at the bottom of the pan, so be sure to deglaze with water, stock, or even alcohol for a bit of extra flavor.

Make it a Meal

This sweet delicacy is most often known for topping burgers or accompanying a juicy piece of steak, like a filet mignon (along with Sautéed Mushrooms!)

There are also quite a few other dishes that can be taken over-the-top with the addition of the rich, buttery flavor these onions bring to the table: 

• Salmon Burgers
• Butternut Squash Pizza
• Honey Balsamic Chicken
• On a baguette with Tomato Bruschetta