French Onion Portobello Mushroom

I am working on mushrooms right now. I am trying to teach the Bean to love them. What is it about kids and mushrooms? What do the little folk have against them? Is it the taste? The texture? The whole fungus thing? Or maybe I’m blaming the poor mushrooms when I should be blaming myself: should I have been pureeing portobellos when the Bean was new to solids?

Whatever the source of mushroom aversion, I am determined that my Bean will overcome it. And this just may be the recipe that clinches it.


I will say that I am just a little proud of this recipe.  And pretty excited about sharing it. Because it’s good. Like really really good with gruyere cheese on top. Imagine a bowl of french onion soup. In a portobello mushroom. Are you with me yet? If the Bean doesn’t like this, then I give up.

These mushrooms are simple enough to pull together for a weekday veggie night, and sided with a simple salad, will make a full meal. But they would be equally at home beside some grilled flank steak, sauteed spinach, a glass of cab sauv and an episode of Shark’s Tank. (I speak from experience.)


For the extra-quick-six-oclock-scramble version of this dish: caramelize the onions in advance (they keep for days in the fridge and even longer in the freezer); soften the mushrooms and grate the cheese the day before. Then just assemble, broil and serve. And watch your kiddos surrender to the mushroom (fingers crossed).

French Onion Portobello Mushroom

Prep Time: 30 minutes

Cook Time: 10 minutes

Total Time: 40 minutes

Yield: 4 servings

Serving Size: 1 mushroom

These gooey just-like-french-onion-soup mushrooms are tasty on their own, or as a side-dish for grilled meat, chicken or fish.


  • 4 large portobello mushrooms, cleaned and stem removed
  • 4 onions, sliced into half moons
  • 1/2 tbsp grapeseed or extra virgin olive oil
  • 2 tbsp butter
  • 1 cup grated gruyere cheese
  • 4 small slices french or sourdough bread
  • 2 green onions, finely chopped (optional)


  1. Preheat oven to 350 F.
  2. Combine butter and preferred oil in a skillet over med-high heat (I used my cast iron for this). When butter is melted, add onions. Cook, stirring occasionally and gradually reducing the heat to low, until the onions are very brown and caramelized, about 30 minutes. (You can let the onions caramelize while you prepare the rest. They don't need your constant attention!) Add a bit of water if they start to dry out.
  3. Brush mushroom caps with bit of oil and then bake them on a baking sheet (lined with parchment if you wish) for about 10-20 minutes, or until they soften and start to release a bit of liquid. Remove from oven. Turn oven to broil.
  4. Divide cooked onions between the mushrooms, spreading them out. Top with a slice of bread and 1/4 of the grated cheese. Return to the oven and broil until the cheese starts to bubble and brown (time will depend on your broiler -- just watch carefully!). Garnish with green onions, if using. Serve immediately on their own or with a little green salad.


To make ahead, caramelize the onions up to several days in advance and/or soften the mushrooms a day or so in advance as well. Then all you have to do is assemble and broil.

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