Caramelized Onion Stuffed Mushrooms will be one of your favorite appetizers when you want to impress any mushroom lover. No sugar is added. The ultimate combination of sweet onions paired with Swiss cheese will have you hooked!
I absolutely love stuffed mushrooms. You can fill them with just about anything and I’ll eat them. They are the perfect bite-sized vehicle to hold all of your favorite toppings. They’re also a wonderful appetizer or party food that will make your guests come back for more. The combination of the Swiss cheese and onions are similar to French onion soup, only it’s stuffed in a mushroom. How perfect is that?
The caramelized onions are cooked slowly until they turn into a sweet, soft flavorful jam. No sugar is added to make them sweet. Cooking them slowly releases all the natural sugars, making them perfect for not only these mushrooms, but as a topping or in a dip.
Although these onion stuffed mushrooms are easy to make, caramelizing the onions does take a little time – however, it’s totally worth it! Trust me on this one. If you don’t have the time or want to skip making the onions yourself, you can always buy a jar of onion jam making this appetizer even easier. Buy a good quality onion jam, please. You’re worth the very best, aren’t you?
I know it’s against the rules to wash mushrooms, but they are dirty so I give them a quick rinse and dry them with paper towels. The “proper way” is to use a paper towel or a mushroom/vegetable brush to wipe away the dirt. If you want to do that then, by all means, wipe away. I find it silly and seriously, does it really “wash” away all the dirt? I have eaten food containing mushrooms – whether stuffed or in salads – where I knew the mushrooms were wiped rather than quickly rinsed. Let me tell you, it wasn’t pleasant when I heard the crunch of dirt in my mouth.
The reasoning behind the “wipe method” versus the “rinse method” is preventing the mushrooms from becoming soggy as they are similar to a sponge. A quick rinse does the job. Just pat them dry afterwards and you are good to go.
I use grated Swiss, but you can use Gruyere or Jarlsberg if you’d like. It’s best if you grate the cheese yourself, as the end result is creamier and rich in both flavor and texture. Yes, it’s easier to buy grated, but it only takes a few minutes to do it yourself.
When I first made these stuffed mushrooms, I simply stuffed them with onions then topped with cheese and baked. They were incredible. The only thing is some of the mushrooms were large in size, making it impossible to take a bite of the mushroom without taking off the entire layer of cheese. The only thing I changed and would recommend is using regular sized mushrooms and not stuffing sized. That way, you can pop these bad boys in your mouth and enjoy the explosion of flavors and textures all in one bite.
Make these caramelized onion stuffed mushrooms at your next gathering and watch people go nuts over them. The onions can be made days ahead. You can also stuff the mushrooms ahead of time and then pop them in the oven when you are ready.
Want more great easy appetizers? Try:
- Sweet and sour kielbasa – it’s made in a crockpot and you set it and forget it. A real crowd pleaser!
- How about some strawberry basil brie bites? These are no cook!
- Bacon wrapped dates with almonds may sound strange, but they’re delicious!
- My port wine cheese ball is another crowd pleaser.
- There’s always the ultimate party favorite – Dips!
Be happy, eat well.
Prep time includes time for caramelizing onions. You can cut this time by 30 minutes if you use premade caramelized onion jam which can be purchased at specialty stores.
The onions can be made days ahead. You can also stuff the mushrooms ahead of time and then pop them in the oven when you are ready.
- 2 medium-large sweet onions *See Note
- 1 tablespoon butter
- 1/2 teaspoon kosher salt
- 1/4 teaspoon pepper
- 1 tablespoon balsamic vinegar
- 24 whole white button or cremini mushrooms washed and stems removed
- 1 tablespoon olive oil for drizzling
- ½ cup freshly grated Swiss, Gruyere, or Jarlsberg cheese about 2 ounces or so
Peel the onions and slice them in half from root to stem. Notch out the root and slice the onions into 1/4” slices. When slicing, slice in the direction from root to stem.
In a large skillet over medium heat, melt the butter then add onions. Sprinkle with salt and pepper and cook for 15 minutes, stirring occasionally. You may need to lower heat if onions are browning too quickly. After onions are lightly browned and a fond develops on the bottom of the pan, reduce heat to low and continue cooking for another 10 minutes. The fond is the brown coating on the bottom of the pan from the sugar drawn out from the onions.
Add balsamic vinegar to deglaze pan, scraping up the fond as it loosens.
Cook the mixture for another 3 - 5 minutes, scraping and deglazing skillet. Remove from the heat and set aside to cool.
Preheat oven to 400 degrees.
Place the mushrooms bottom side up in a baking dish and drizzle with the olive oil.
Stuff the cavity of each mushroom with the caramelized onions, then sprinkle tops with cheese.
Bake for 15 to 20 minutes. Serve warm.
You can use premade onion jam found in specialty stores.