Caramelized Onions and Mushrooms are an excellent topping for steak, prime rib, filet mignon, hamburgers, and virtually any cut of meat! Prepare this delicious condiment ahead of time for an unforgettable meal!

Stainless steel skillet with sauteed mushrooms and onions with fresh herbs to the side.

If you’re a steak lover like me, these caramelized onions and mushrooms are a must-make! They level up any cut of beef in a way that is truly otherworldly.

Melt in your mouth caramelized onions paired with earthy mushrooms and a splash of balsamic vinegar results in that buttery tangy explosion of flavor that sends your taste buds to the moon.

Whether we’re making casual Perfect Grilled Steak on the weekends, or Beef Tenderloin, Filet Mignon, or Garlic Butter Prime Rib for special occasions, this easy dish is sure to be included.

Essentially, where there’s beef, there’s this.

While the caramelization process can take anywhere from 45 to 60 minutes to complete, the process is hands off enough that you can multitask while everything is cooking.

And trust me, this simple recipe is well worth the cooking time!

If we’re making steak or burgers or something that finishes quickly, we start caramelizing the onions long before we begin preparing the meat.

When making prime rib, sauteed onions can easily be prepared while the prime rib is roasting in the oven. 

Vertical image of a close up shot of a forkful of prime rib, mushrooms, and onions.

You’re going to love what this tasty addition does to your whole experience of beef!

Let’s chat about the simple ingredients to make caramelized onions and mushrooms.

Ingredients for Caramelized Onions and Mushrooms:

Avocado Oil: Used to sauté the onions and mushrooms, a quality high-temperature cooking oil will guarantee the best result. Because avocado oil has neutral flavor and can be used at high temperatures, it is ideal in applications like this.

If you only cook with olive oil, feel free to make the substitution but be careful not to burn the oil.

I don’t recommend using butter at the onset to cook the vegetables because the initial high temperature and the long cook time will burn it. It’s best to add butter at the end for this reason.

Yellow Onions: Fresh onions get cooked to perfection in a large sauté pan, allowing the natural sugars to release such that the onions become soft and buttery.

Because onions cook down so much, we need at least two in order to make the long process worthwhile. If you’re serving more than 4 people, consider using 3 large onions but stick with the same amount of mushrooms.

Sweet onions, white onion, and red onions all work! I find yellow onions have the best caramelization effect but any kind of onions will be great.

Mushrooms: Chopped baby bella mushrooms get added to the sauteed onions once they are almost fully caramelized. This ensures the onions have enough time to soften and become nice and buttery. Use white mushrooms if you prefer them.

Salt and Black Pepper: Use sea salt according to your personal taste. I sprinkle both the onions and the mushrooms with salt once they go into the skillet to help coax out their internal moisture and to season everything.

Garlic Powder: Because we’re cooking the vegetables for so long, I find it easiest to use garlic powder instead of fresh garlic so that I don’t have to keep track of it and keep it from burning. Dried minced garlic is also a great option!

Balsamic Vinegar (or Red Wine): Used to add even more richness and tang, balsamic vinegar makes caramelized onions taste simply sensational! You won’t regret the addition! If you love cooking with wine, you can swap the balsamic out for a dry red wine such as cabernet sauvignon or malbec. White wine such as sauvignon blanc works too.

Butter: As an option, you can add a pat of butter at the end of the cooking process to bring that yummy creamy flavor to the onions and mushrooms. If you’re dairy-free, feel free to leave it out.

The end result is the best caramelized onions to enjoy as an easy side dish to your impressive main course. This versatile side dish is a great way to level up a steak dinner during the holiday season.

Vertical image of finished sauteed onions and mushrooms.

Optional Additions:

  • Rather than using garlic powder or dried minced garlic, you can use 3 cloves of fresh garlic that has been finely minced. Just be sure to add them about 10-15 minutes before the end of cooking so that they have time to soften up but don’t burn during the cooking process.
  • Cook 4 to 6 strips of thick-cut bacon and use the grease to cook the onions and mushrooms. You’ll want to keep the crispy bacon to the side, chop it, then add it back in once the vegetables have finished cooking. 
  • If you prefer the flavor of soy sauce over balsamic vinegar, feel free to make the swap. If you do so, don’t add any additional salt as they soy will be plenty salty.
  • Swap out the balsamic for 1 tablespoon of Worcestershire sauce if you prefer.
  • Add fresh herbs such as fresh thyme or fresh parsley if you have some on hand.

How to Caramelize Onions and Mushrooms:

If your mushrooms don’t come pre-rinsed, clean mushrooms well under lukewarm water.

Slice the onions into thin slices. While dicing the onion into chunks will work too, I find the texture is best when the onions are sliced.

Heat the avocado oil in a large non-stick skillet (or a cast iron skillet) over medium-high heat and add the sliced onions.

Note: A stainless steel skillet works too but use extra oil and make sure you don’t cook higher than medium heat to ensure the food doesn’t stick to the skillet.

Sprinkle with sea salt and sauté, stirring occasionally, until the onions begin to sweat, about 5 to 8 minutes. To speed up the process, you can cover the skillet with a lid.

Onions sautéing in a skillet.

Once the onions have become very soft, reduce to medium heat or medium-low heat.

Continue cooking, stirring occasionally, until the onions begin turning golden-brown, about 20 to 30 minutes.

The goal is to slow cook the onions so that they become uniformly golden brown and don’t begin to burn around the edges or stick to the pan. The key here is to start the onions on a high heat to allow them to release some moisture, then lower the temperature once they have softened for the remainder of the cooking process.

If at any time the onions begin to stick to the bottom of the pan, deglaze the pan with a little water, broth, or wine.

Add the sliced mushrooms and cover the skillet.

Mushrooms on top of sauteed onions in a skillet, ready to be cooked.

Cook, stirring occasionally, until much of the liquid has leached out of the mushrooms, about 5 to 8 minutes.

Sauteed onions and mushrooms in a skillet with water coming out.

Once there is a good deal of liquid in the skillet, remove the lid from the skillet and increase the heat to medium-high. Continue cooking and stirring until the majority of the liquid has evaporated.

Now the goal is to allow the liquid to burn off so that the texture of the mushrooms is nice and soft. You’ll know you’re there once some brown bits begin sticking to the skillet.

Stir in the garlic powder, balsamic vinegar, and butter, and continue stirring until the balsamic becomes well-incorporated into the caramelized onions and mushrooms and you’re left with perfect caramelized onions.

Pouring balsamic vinegar into the skillet with sauteed mushrooms and onions.

Serve caramelized onions and mushrooms on top of your choice of steak.

Finished caramelized onions and mushrooms in a skillet.

Store any leftovers in an airtight container in the refrigerator for up to 5 days.

Use sauteed mushrooms and onions as the perfect topping the next time you make Prime Rib, Marinated Skirt Steak, Brisket, Pork Chops, ribeye steaks, and any of your steak recipes or ground beef recipes!

Stainless steel skillet with caramelized onions and mushrooms.

There you have it! Amazing caramelized onions for steak to enjoy whenever the craving calls. May all of your beefs be adorned in caramelized onion bliss!

Stainless steel skillet with sauteed mushrooms and onions with fresh herbs to the side.

Caramelized Onions and Mushrooms

5 from 1 vote
The yummiest topping for steak of any type, caramelized onions and mushrooms are a great side dish to level up any main dish!
Prep Time 10 minutes
Cook Time 50 minutes
Total Time 1 hour
Servings: 4 to 6 Servings

Ingredients

  • 1 Tbsp avocado oil
  • 2 medium-sized yellow onions sliced into thin slices
  • 16 ounces baby bella mushrooms chopped
  • ¾ tsp sea salt to taste
  • ½ tsp garlic powder or dried minced garlic
  • 3 Tbsp balsamic vinegar*
  • 1 Tbsp unsalted butter optional

Instructions

  • Rinse the mushrooms well under lukewarm water.
  • Slice the onions into thin slices.
  • Heat the avocado oil in a large non-stick skillet over medium-high heat and add the sliced onions. Sprinkle with sea salt and sauté, stirring occasionally, until the onions begin to sweat, about 5 to 8 minutes. To speed up the process, you can cover the skillet with a lid.
    Onions sautéing in a skillet.
  • Once the onions have become very soft, reduce to medium heat or medium-low heat. Continue cooking, stirring occasionally, until the onions begin turning golden-brown, about 20 to 30 minutes.
  • The goal is to cook the onions slowly so that they become uniformly golden brown and don't begin to burn around the edges. The key here is to start the onions on a high heat, then lower the temperature once they have softened for the remainder of the cooking process. If at any time the onions begin to stick to the bottom of the pan, deglaze the pan with a little water, broth, or wine.
  • Add the sliced mushrooms and cover the skillet. Cook, stirring occasionally, until much of the liquid has leached out of the mushrooms, about 5 to 8 minutes.
    Mushrooms on top of sauteed onions in a skillet, ready to be cooked.
  • Once there is a good deal of liquid in the skillet, remove the lid from the skillet and increase the heat to medium-high.
    Sauteed onions and mushrooms in a skillet with water coming out.
  • Continue cooking and stirring until the majority of the liquid has evaporated. Now the goal is to allow the liquid to burn off so that the texture of the mushrooms is nice and soft. You'll know you're there once some brown bits begin sticking to the skillet.
  • Stir in the garlic powder, balsamic vinegar, and butter, and continue stirring until the balsamic becomes well-incorporated into the caramelized onions and mushrooms and you’re left with perfect caramelized onions.
    Pouring balsamic vinegar into the skillet with sauteed mushrooms and onions.
  • Serve caramelized onions and mushrooms on top of your choice of steak.

Notes

*Replace the balsamic vinegar with ⅓ cup red wine if you love cooking with wine.
Store any leftovers in an airtight container in the refrigerator for up to 5 days.

Nutrition

Serving: 1(of 4) · Calories: 96kcal · Carbohydrates: 13g · Protein: 5g · Fat: 4g · Polyunsaturated Fat: 2g · Sodium: 458mg · Fiber: 3g · Sugar: 7g
Author: Julia
Course: Side Dishes & Snacks
Cuisine: American
Keyword: caramelized onions and mushrooms, caramelized onions recipe, sauteed mushrooms, sauteed mushrooms and onions, sauteed onions and mushrooms for steak
Did You Make This Recipe?I want to see it! Tag @the.roasted.root on social media!

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Julia Mueller
Meet the Author

Julia Mueller

Julia Mueller is a recipe developer, cookbook author, and founder of The Roasted Root. She has authored three bestselling cookbooks, – Paleo Power Powers, Delicious Probiotic Drinks, and The Quintessential Kale Cookbook. Her recipes have been featured in several national publications such as BuzzFeed, Self, Tasty, Country Living, Brit.co, etc.

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Questions and Reviews

    1. Absolutely! The caramelized onions and mushrooms save very well. Reheat them in a skillet for the best tasting result. I would add a small amount of water so that the veggies don’t dry out when reheating them.