Special Occasion French Onion Mushrooms An elegant appetizer made with onions cooked in the style of French onion soup, lots of swiss cheese, and a portabella mushroom base

Special Occasion French Onion Mushrooms

by Michele Pesula Kuegler | October 12th, 2023 | Appetizers, Recipes, Tapas Monday, Vegetarian

This is a fancy stuffed mushroom!
Black tie not required, but fork and knife definitely are.

portabellas with french onion filling

On Tuesday I shared a new version of French onion mushrooms, which I have coined as everyday. This version definitely is fancier, but it is only because of one ingredient change. Tuesday’s recipe used beef broth; today’s uses sherry. However, that one ingredient change is impactful. First, many people don’t keep sherry in their pantry. Second, the sherry helps develop richer, more robust flavors, making this an appetizer that is perfect for a special occasion.

To learn more about this recipe, first published in April 2016, keep reading.

The naming of a recipe can be tricky. Take today’s recipe as an example. I decided to call it French onion mushrooms. It has many of the flavors of French onion soups- loads of onion, rosemary, and sherry. However, it isn’t made with any meat (as this is vegetarian week), and for many it isn’t French onion without the beef stock. I’m guessing some food people would tell me the name is inaccurate; to me it is reminiscent of French onion soup, so I’m keeping the name.

When I was playing with this recipe, I wasn’t aiming to make it vegetarian. It just ended up that way. I used it as a hearty appetizer in a Tapas Monday menu. Served with crusty bread and a salad, it was a great meal for two. Of course, if it weren’t a Monday night, you probably could call them entrées instead. Depending on your diner’s appetite, you’ll need one or two. Also, if you’re thinking of using them as appetizers at a cocktail party, I’d suggest using baby bellas, so they are almost bite-sized and easier to fit on a plate full of snacks.

As far as the recipe goes, the sherry is essential. For me it is a key part of turning caramelized onions into French onion soup. A small bottle should be relatively inexpensive at your local grocery store. The sugar is optional. I know many cooks believe that caramelized onions shouldn’t need to have sugar added. I personally like the taste it provides. You do what you prefer.

Regardless to sugar or not, this is a recipe you have to try. All things considered it’s fairly healthy. It also is incredibly delicious. Why not try making a batch in the near future?

Special Occasion French Onion Mushrooms

Michele Pesula Kuegler

Prep Time 10 minutes
Cook Time 30 minutes
Total Time 40 minutes

Course Appetizer

Servings 4



  • 4 portabella mushrooms
  • olive oil
  • 1/2 tablespoon butter
  • 2 cups sliced sweet onion
  • 1 teaspoon fresh rosemary minced
  • 1 teaspoon sugar optional
  • 1/4 cup fino sherry
  • 4 ounces swiss cheese shredded



  • Preheat oven to 425.
  • Clean mushrooms, remove stems, and brush lightly with olive oil.
  • Place mushrooms cap side down on a rimmed baking sheet.
  • Bake for 8 minutes; flip and bake for an additional 4-6 minutes. Remove from oven.
  • While mushrooms bake, melt butter in large frying pan over medium heat.
  • Reduce heat to medium-low, add onions, sautéing for 20-25 minutes, or until golden brown.
  • Add rosemary, sugar, and sherry, and saute for another 5 minutes.
  • Preheat broiler.
  • Place mushrooms cap side down on baking sheet, and divide onion mixture among the mushrooms.
  • Top with swiss cheese.
  • Place baking sheet on upper most rack in the oven, and broil for 30-60 seconds or until cheese is melted.

Keyword stuffed mushrooms
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