Name: Caramelized Onions and Mushroom, Great for Burgers & Grilled Veg
Prep time: 5 min
Cook time: 25 min
Total time: 30 min
Ingredients: 1 large yellow onion (sliced); 8 oz mushrooms (baby bella or white, sliced (227 grams)); 2 teaspoons olive oil; ¼ teaspoon salt

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This caramelized onions and mushroom is perfect for burgers, steak, and grilled veggies. Just 4 ingredients, a how-to video & step-by-step photos included!

Flat lay of caramelized onions and mushrooms with sprinkled salt and parsley, perfect for burgers and steak.

Why You Will Love This Caramelized Onions and Mushroom

It’s packed with flavor!
Adding it to any dish will make it a gourmet-like experience
- Perfect as sides for your (vegan) burgers, steak, grilled vegetables, wraps, you name it!
It only requires 4 ingredients, 2 of which you should already have at home
With minimal oil, this recipe is way healthier than your usual caramelized mushrooms and onions
100% plant-based, vegan, vegetarian, you name it

Watch the Recipe Video!

Ingredients

Just 4 simple ingredients, but so much flavor in this sautéed caramelized mushroom and onion!

Yellow onion: For that deep, rich, caramelized flavor. You can use other types of onions such as red onions and shallots.
Mushrooms: The second star ingredient!
Olive oil: Adds even more flavor to this dish.
- Feel free to sub this with vegan butter or avocado oil if that’s what you have at hand.
Salt: A bit of salt to amp up the flavor.

Baby bella mushrooms, a yellow onion, olive oil, and salt in small white bowls with labels.

What Kind of Onions Can I Use?

Any kind of onion will work 😊 The taste will vary slightly but you will still get that deep, rich, caramelized flavor. You can even use a combination of different varieties!

What Kind of Mushrooms Can I Use?

Use either baby bella mushrooms or white mushrooms. I find that baby bella mushrooms have a ‘meatier’ taste while white mushrooms have a slightly sweet note to them.

P.S. If you like mushrooms, I’ve written a thorough post on 35 Brown Vegetables, which also includes 6 different types of mushrooms!🍄

Instructions / How to Caramelize Onions for Burgers

Slice: Slice both the onion and the mushrooms.

For the onion, you want to prevent cutting through the root to prevent releasing the chemicals that make you cry. To do so, first cut it in half, right next to the root (but NOT through it). Then peel the skin off.

Next, with your knife facing the root, thinly slice the onion into 0.25 to 0.5 inch (0.6 to 1.3 cm) slices. Again, without cutting through the root. See the video below in the recipe card for a demonstration. (PS Thank you Gordon Ramsay for sharing this trick!)

For the mushrooms, slice them into 1cm (0.4 inches) thickness.

Cutting a yellow onion into two, next to the root. — 1. Cut next to the root, but not through it

Cut up yellow onion with the skin removed. — 1. Cut next to the root, but not through it

Add onions first: Heat the olive oil in a large pan / cast iron skillet over medium heat. Then brown the onions first for about 5 minutes, until you get those fragrant sautéed onions. As always, aromatics should go first in the pan!

Add mushrooms: Now it’s time for the sliced mushrooms to go into the pan! Continue cooking for 20-25 minutes on low heat. It should already look golden brown in the first 10-15 minutes (see picture #3 below).

Keep an eye out: If it starts to look dry, splash 1 Tablespoon of water to deglaze. Only add 1 Tablespoon at a time because if you have too much liquid in your pan, they will steam instead of caramelize.

Salt: After 25 minutes, sprinkle the salt, stir, and turn off the heat to serve! Garnish with some fresh herbs such as parsley or thyme if you like!

Sautéed yellow onion on a black frying pan. — 1. First sautée the onions

Sliced yellow onion and baby bella mushrooms after sautéeing for 10 minutes on a black frying pan. — 1. First sautée the onions

What are some tricks to caramelizing onions and mushrooms?

Avoiding soggy caramelized onions – Here are some reasons why this might be the case:

The pan is overcrowded such that the moisture cannot evaporate, creating more of a steaming effect instead of caramelizing.
You add salt early on during the cooking. Salt draws out moisture from the onions and mushrooms into the pan. So no, do NOT salt your onions while caramelizing.
You sautéed them in high heat instead of low / medium low heat. When you cook them in high heat, they are also more prone to burning

Should I cook onions or mushrooms first? – Onions first.

If cooking mushrooms first: Mushrooms release quite some moisture when cooked. So if you add mushrooms first, make sure that all water has evaporated before you add your onions. Otherwise, you might end up with soggy caramelized onions.
If cooking onions first: Although there is a bit more risk of the onions getting soggy since mushrooms will release moisture once the onions are in the pan, there is also some deglazing effect happening here, giving you umami flavor. Onion also takes longer to caramelize. Moreover, as a general rule, aromatics should go first whenever cooking any dishes.

Should you cover onions when caramelizing? – Nope, don’t do this. Covering the pan traps the liquid and it will steam instead of caramelizing the onions and mushrooms.

Caramelized mushrooms and onions, perfect for burgers and steak.

What Pairs Well with Caramelized Onions?

I like to pair this caramelized mushrooms and onions recipe as fillings for my veggie smash burgers, vegan steak, sandwiches (such as in this Hummus Bagel Sandwich recipe), and wraps.

You can also serve this as a side dish with mashed/grilled potatoes, my 3-Ingredient Vegan Mac and Cheese, my Healthy Garlic Bread, or Garlic Bread with Regular Sliced Bread recipe.

Storage and Meal Prep Instructions

Storage and Meal Prep: These caramelized mushrooms will last up to 5 days in the fridge so you can prepare ahead for the whole week.

It’s the perfect recipe to batch-cook in the weekend. You will be super excited for your next meal just thinking about how much flavor this caramelized mushroom and onion packs!

Freezing: Freeze in an air-tight container for up to 3 months. Use small containers, or even ice cube trays or muffin tins to make it easier to heat up. To heat up, just give them a quick stir fry in a pan. You can also microwave them when pressed for time.

How Do You Reheat Caramelized Onions?

You can quickly stir-fry the caramelized onions and mushroom again just before serving. Add splashes of olive oil or water to prevent them from sticking to the pan. Heat until everything is warm, for about 3-5 minutes depending on the portion size.

You can also simply microwave it for 30 seconds up to 2 minutes, depending on the portion size.

FAQ

To put this simply, often enough so that it doesn’t get burned, but not too often so it can caramelize. I stir mine about every 5 minutes, but this will also depend on the exact type of pan that you’re using.

If you’re new to cooking, it’s better to stir it more frequently. This way, you might take more time until the onions are properly caramelized, but you would prevent burning which is irreversible!

Caramelize your onions on low heat instead. If the heat is bigger/stronger, you might risk burning. But you might need to caramelize your onions on medium heat if you are cooking a big batch.

Vinegar (such as balsamic vinegar or apple cider vinegar) is added to caramelized onions for some acidity, which can help balance out their sweetness and enhance their flavor. However, I don’t find it necessary so I’m skipping it.

No, you don’t. The onions naturally contain sugars that will caramelize during the cooking process.

Yes, you can! Mushrooms can be cooked / sautéed for quite a long time without getting mushy. So you can add them early on when cooking, just like what I did in this caramelized onions and mushrooms!

A close-up shot of a fork holding a caramelized mushroom with more caramelized mushroom and onions in the background.

Want More Mushroom Recipes?

Try my vegan bulgogi mushrooms or this shiitake mushroom sushi recipe!