Caramelized Mushrooms and Onions

caramelized mushrooms and onions in a cast iron skillet on a beige cloth

Caramelized mushrooms and onions are a delicious and very enjoyable way to include more veggies into your day. As a dietitian, I am a firm believer that vegetables should taste great, and that includes investing a little time into cooking them properly.

This mixture of caramelized mushrooms and onions requires just a little bit of patience, but the end result is well worth it. They’re so good and they pair well with chicken, burgers, salads, pasta, eggs–the list is endless.

caramelized mushrooms and onions with sprig of thyme in a skillet

What You’ll Need

mushrooms, onions, butter, olive oil ingredients

Onions: I like to use yellow onions because of their sweetness, but red onions are delicious caramelized, too! With just a little time, these onions turn gooey and delicious.

Mushrooms: I used whole baby bella mushrooms and washed and sliced them. However, feel free to use pre-sliced mushrooms for convenience.

Fat: This recipe uses a combination of olive oil and butter for fat. This gives off the delicious, salty flavor from the butter, but helps prevent burning by using a combination of fats, since olive oil has a higher smoke point than butter.

Balsamic vinegar: I like to add just a bit of balsamic vinegar at the very end of the caramelization process to help deglaze the pan as well as add some flavor.

caramelized mushrooms and onions close up in a cast iron skillet

How to Make Caramelized Mushrooms and Onions

  1. Prepare the mushrooms and onions. Wash and dry the mushrooms well. Slice both the onions and mushrooms into quarter inch slices.
  2. Heat the fat in a skillet. Heat the olive oil and butter on medium heat. Using this combination of oils gives great flavor and helps prevent burning.
  3. Cook the mushrooms and onions. In order to caramelize the mushrooms and onions, you will need to let them cook and only stir every five minutes, redistributing the mushrooms and onion mixture and scraping the bottom of the pan.
  4. Serve and enjoy! These caramelized onions and mushrooms go perfectly with so many dishes.
process of making caramelized onions and mushrooms

Notes & Tips

caramelized mushrooms and onions on a fork

Storage & Reheating

These caramelized mushrooms and onions can be stored in an airtight container in the refrigerator for up to a week. Simply reheat in the microwave or toss into dishes just before they are finished cooking.

mushrooms and onions in cast iron skillet

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caramelized mushrooms and onions in a cast iron skillet on a beige cloth
Print Recipe
5 from 1 vote

Caramelized Mushrooms and Onions

Caramelized mushrooms and onions are a delicious topping with endless possibilities. Pair them with burgers, chicken, salads, pasta, eggs, and more!
Prep Time5 minutes
Cook Time40 minutes
Total Time45 minutes
Course: Side Dish
Cuisine: American
Keyword: burger topping, caramelized mushrooms and onions, caramelized onions, easy
Servings: 6 servings
Author: Kate Reeder


  • 2 medium yellow onions
  • 8 oz package baby bella mushrooms
  • 2 tbsp salted butter
  • 2 tbsp olive oil
  • 1 tsp balsamic vinegar


  • Start by slicing the onions and mushrooms. Make sure the mushrooms have been washed and dried well. Slice the mushrooms and onions into ¼ inch slices. See recipe notes for tips on properly slicing onions.
  • In a stainless steel or cast iron skillet, heat the butter and olive oil on medium heat.
  • Add the sliced onions and mushrooms and stir to evenly coat in the fat.
  • Without stirring, let the onions and mushrooms cook for five minutes. After five minutes, stir them, scraping the bottom of the pan. If they seem to be burning at all, reduce the heat slightly.
  • Continue this process, letting them cook for five minutes at a time, then stirring and scraping the bottom, until the mushrooms and onions are dark, soft, and caramelized (about 35-40 minutes).
  • Add the balsamic vinegar, stir, and remove from heat.


  1. To slice the onions, chop the onion in half (slicing from stem to root). This should result in two identical halves. Then, remove the peel, leaving the root intact (the root is the end that has the thin, hairy, dried roots). Then, lie each side flat and chop off both ends. Now, slice the onion halves into ¼ inch thick slices, slicing from stem to root.
  2. Use a cast-iron or heavy stainless steel skillet at least 10-12 inches wide. This helps avoid overcrowding the pan, and allows the heat to be evenly distributed.

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