These sweet and savory Portobello Mushroom and Caramelized Onion Sliders will have you wanting more! Portobello mushrooms marinated in balsamic vinegar and Dijon mustard with sweet caramelized onions on your favorite bun, what's not to love?
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I have been wanting to make a portobello mushroom sandwich for the blog for a while now. These Portobello Mushroom and Caramelized Onion Sliders are finally getting a debut because I was on a sandwich-making kick recently.
I fell in love with portobello mushroom sandwiches on my first trip with my husband. This was quite a few years before I knew I was gluten intolerant so there were more options for me eating out.
On the trip I had three vegan portobello mushroom sandwiches at three different restaurants because they looked like the best choice on each of the menus.
I was happy with every single one of them and not at all tired of eating the same thing several times on the trip.
The ingredients that add a ton of flavor to the mushrooms are balsamic vinegar and Dijon mustard.
Not only are the mushrooms marinated in balsamic vinegar and Dijon mustard, but they are also cooked down in the marinade as well.
You may taste the mushrooms and think that the flavors are quite strong, but once you combine them with your favorite buns and some sweet caramelized onions, you will taste the symphony of flavors that the mushrooms become part of.
Caramelized onions are one of those ingredients that elevate anything that you add them to. In fact, I would recommend doubling the amount so that you can use them in other dishes.
Tips
- For caramelized onions you need some patience. It takes a good 40 minutes to get nicely browned onions. Slow and steady wins the race.
- If the onions start to stick, add a little water, like a quarter of a cup or so.
- Balsamic vinegar adds a wonderful flavor to caramelized onions. I always add a couple of splashes near the end of the cooking time.
- Make a double batch of the caramelized onions and add them to a Vegan Caramelized Onion and Mushroom Grilled Cheese, a baked potato, or Vegan Mashed Cauliflower with Caramelized Onions and Mushrooms.
- Make a double batch of the whole recipe and add half of it to pasta with the Maple Dijon Mayo and some steamed asparagus.
- Cook mushrooms in marinade for more intense flavor.
- The type of bread / buns that you use makes a big difference in the overall taste of the sandwiches.
Other Vegan Sandwiches
The combination of flavors in these vegan portobello mushroom sliders is rich and satisfying. If you love this recipe, please come back and leave your feedback and star rating.
📋 Recipe
Portobello Mushroom and Caramelized Onion Sliders
Ingredients
Portobello Mushrooms
- ½ cup balsamic vinegar
- 3 tablespoons Dijon mustard
- 2 tablespoons olive oil
- 2 portobello mushrooms
- Salt
Caramelized Onions
- 2 cups sliced onion
- 2 tablespoons olive oil
- 2 tablespoons balsamic vinegar
- Salt
Maple Dijon Mayo
- ¼ cup vegan mayo
- 2 tablespoons Dijon mustard
- 2 tablespoons maple syrup
- Buns - I used Pamela's gluten free pizza mix
Instructions
Caramelized Onions
- Add olive oil to a hot pan. Add sliced onion and cook on medium-low heat for about 35-40 minutes, or until onions are caramelized. Add balsamic vinegar to deglaze the pan. Add salt. Remove onions.
Portobello Mushrooms
- Wipe mushrooms with a damp towel and slice into ½ " slices. Mix balsamic vinegar, Dijon mustard, and olive oil. Marinate the mushrooms for at least an hour.
- In the same pan that you cooked the onions, place marinated mushrooms and marinade. Cook on medium heat until mushrooms are tender and marinade is cooked down.
Maple Dijon Mayo
- Mix all ingredients.
- Slather Maple Dijon Mustard on buns. Add portobello mushrooms and caramelized onions.
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Nutrition
*Note: Nutrition information should be considered an estimate only. Different nutrition calculators give you different results. Also note that the buns were not calculated into the nutrition info.
Sienna says
I enjoyed this greatly and found the recipe Delish just as it is!
Willow Moon says
Thanks Sienna!
Sarah says
Way, way too much balsamic in the marinade, and I found the combo of balsamic and dijon mustard off-putting. Others agreed. Next time I'll eliminate the dijon mustard, use half the balsamic, and figure out something to cut the vinegar a little, maybe more oil and/or water. I made a triple batch for a party (25 people) and it was not a hit. The caramelized onions were good and I would make those again.
Willow Moon says
Hi Sarah, I'm sorry you didn't like them!
Emily says
I'd love to try these for an event...
Can the mushroom/onion be made ahead of time and stored?
Willow Moon says
Yes, you can store them in an airtight container in the fridge for up to 5 days. If you worried about how they'll taste when reheated you might want to make some before the event and test it out.
Mary says
Wow these were absolutely amazing..I will be making these again…thank you for sharing
Willow Moon says
Thanks Mary, I’m so glad you liked them!
Liz says
Truly and absolutely delicious! I did add a little maple syrup while the mushrooms were cooling down as I found them to be a tiny bit too vinegary and that adjusted the flavors. Absolutely great!
Willow Moon says
Thanks so much Liz! I'm glad you were able to tweak the recipe to your liking!