Learn how to caramelize onions with this step-by-step tutorial! Caramelized onions add tons of savory richness to countless recipes. When prepared correctly, they have a perfect balance of sweetness and bitterness. Let’s take an in-depth look at how to caramelize onions, my top tips for perfect results, and some of the many wonderful ways you can use them to enhance your recipes!
On the first day of culinary school, we learned two important techniques: how to make chicken stock and how to caramelize onions. I realized during that lesson how much these classic techniques can make a difference in recipes. Learning how to properly caramelize onions will take your cooking to the next level with very little effort.
Caramelized onions are savory and rich, with a complementary balance of sweetness and bitterness. If they’re not caramelized enough, they can make a recipe too sweet. On the flip side, too much caramelization can lead to burnt, bitter results.
You’ll find a printable recipe at the end, but I highly recommend reading through the more detailed step-by-step instructions in this post for perfect results every time! Understanding the why behind specific ingredients and recipe steps is the key to becoming a better home cook.
How to Caramelize Onions
Most of the time, caramelized onions are cut into thin, “half-moon” slices before caramelizing. I recommend reading my tutorial on how to chop an onion. While it covers chopping an onion into pieces instead of slices, it goes over some basic techniques to help get you started (how to hold your knife, protect your fingers, etc).
You can also watch my video on how to slice an onion into half moons to see how I cut onions specifically for caramelizing:
Step 1: Place onions in a large skillet over low heat.
I typically use a large flat-sided skillet for caramelizing onions, also known as a sautoir. I prefer the flat-sided version since it’s easier to caramelize a large quantity of onions at once. However, you can also use a regular large skillet or something like an enameled cast iron Dutch oven.
Tip: Onions shrink down by more than half when caramelized. Always caramelize more onions than you think you’ll need.
Whichever skillet you use, avoid using a nonstick pan. You want to use something like stainless steel or cast iron. More on that when we get to Step 2.
Once the skillet is warm, add a thin layer of olive oil or clarified butter, followed by the onions and a pinch of salt. Salt helps extract water from ingredients (this is why eggplant is often salted before cooking). Removing water helps the onions caramelize faster.
Step 2: Allow a glaze to form on the bottom of the pan.
Are you familiar with the culinary terms glazing and deglazing? These are the foundation of caramelizing onions! You’ll be able to see this process in action if you watch my video below.
How Glazing/Deglazing Works: As the onions cook over low heat, brown bits will begin to form on the bottom of the pan. Once the glaze has formed (also known as “fond”), you “deglaze” the pan by adding a small amount of water. The liquid will loosen the fond, and you’ll be able to easily scrape it up and stir it back into the onions.
Glazing and deglazing doesn’t work nearly as well in nonstick pans.
The nonstick coating prevents a glaze from properly forming. While the onions will caramelize eventually, it takes a much longer time. I recommend using stainless steel, aluminum, or cast iron (seasoned or enameled).
Tip: Stir the onions occasionally, but not too often because leaving the onions alone will help the glaze develop on the bottom of the pan.
Step 3: Deglaze the pan.
Keep a liquid measuring cup full of water next to the skillet. When it’s time to deglaze, pour out a small amount, maybe 1-2 tablespoons.
Once the water hits the pan and sizzles, use a spatula or wooden spoon to scrape the bottom of the pan, detaching the brown bits and stirring them back into the onions.
There’s no need to measure the water. If you add too little, you’ll be able to tell because the liquid will evaporate before you’ve had a chance to scrape up the fond. Simply add more. If you accidentally add too much water, it will evaporate and the onions continue to cook!
Step 4: Continue glazing and deglazing.
The rest of the process requires patience. Allow the glaze to build, stirring occasionally, and then deglaze with water. This can take up to 45 minutes.
It’s a good time to multitask; you don’t need to stand over the stovetop the entire time. Just keep an eye on the onions while you do the dishes or cook the rest of your meal.
Step 5: Cook until the onions are a deep brown color.
After 30 minutes, start tasting the onions. You’ll know they’re ready when they reach a perfect balance of sweet and bitter. It may take up to 45 minutes (some recipes even call for an hour).
When the onions taste balanced, they’re done. You can add a splash balsamic vinegar or chopped fresh thyme for extra flavor, but the caramelized onions will be amazingly delicious as is.
Remember how full the pan was in the first photo? Look how much they cooked down!
If you’ve never caramelized onions before, how do you know when they’re done? It’s all about flavor balance. Again, caramelized onions should be a perfect balance of sweetness and bitterness.
Have you ever ordered French onion soup at a restaurant, only to find it was too sweet? Or perhaps a caramel dessert that tasted too bitter?
When an onion hasn’t been caramelized enough, it can be extremely sweet. Or, if you push the caramelization too far, they’ll have an unappealing bitter taste. The key is to taste as you go.
Also, I recommend scraping up the brown bits with a firm spatula or wooden spoon, as opposed to a softer silicone or rubber spatula. This one is my favorite. A metal fish spatula will also work, but it might scratch the bottom of your pan a bit.
What Kind of Onion is Best to Caramelize?
You can caramelize any type of onion, as well as shallots and leeks, all using this exact method. For a good, all-purpose option, I recommend using yellow onions for the best results. They have a neutral flavor that’s not too sweet.
The possibilities for caramelized onions are truly endless! Here are a few of my favorites
- Use as a topping on your favorite sandwich
- Top crostini with goat cheese and caramelized onions for a quick appetizer
- Add to grilled cheese
- Use as a pizza topping
- Add to mac and cheese
- Use in a savory tart (try my Apple, Cheddar and Caramelized Onion Galette or Spinach, Artichoke and Caramelized Leek Tart)
- Use in Thanksgiving stuffing
- Add to savory oatmeal (yes, that’s a thing)
Can You Freeze Caramelized Onions?
You can freeze caramelize onions, and I recommend it! Once frozen, you’ll be able to use them quickly without the long cook time.
I recommend freezing the onions in a resealable plastic freezer bag. Let the onions cool completely first, then place in the bag, press flat, and freeze.
You can add them directly from the freezer into soups and stews, or let them thaw on the counter, refrigerator or using the defrost setting on your microwave.
More Cooking Tutorials
- 4 large or 5 medium yellow onions (other onions may be substituted)
- 1 tablespoon extra virgin olive oil, or as needed
- 1/8 teaspoon kosher salt (a pinch)
- Slice the onions into half moons. Cut off and discard the stem end of the onion, then lay the flat end on the cutting board. Slice in half from root to tip. Peel away the outer layers of skin, place each half flat-side down on the cutting board, and slice into thin half moon strips, discarding the root ends. Repeat with the remaining onions. (Note: see my post for a video demonstration of this process).
- Place a large stainless steel, aluminum or cast iron skillet (do not use nonstick) over low or medium-low heat. Once the pan is warm, add just need enough oil to create a thin coating on the bottom of the pan. Have a small liquid measuring cup with water nearby.
- Add the onions along with a pinch of salt, and cook, stirring occasionally, until some brown bits begin forming on the bottom of the pan, 4-5 minutes. The less you stir, the faster the brown bits will start to form. However, you do want to stir occasionally for even cooking and to prevent burning.
- Once the brown bits (aka fond or glaze) have accumulated and darkened but are not yet starting to burn, add a splash of water to deglaze the pan (1-3 tablespoons; just enough to loosen up the fond). Use a firm spatula or wood spoon to scrape up the brown bits and stir them back into the onions.
- Repeat this process of glazing and deglazing for around 45 minutes. As the caramelization process moves further along, the process will speed up; you'll need to stir and deglaze more often.
- Continue cooking until the onions and a rich brown color and they taste like a good balance of sweet and bitter.
- Store in an airtight container in the refrigerator for 3-4 days, or in the freezer for up to 3 months.
Please read my full post for additional recipe notes, tips, and serving suggestions!
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