French Onion Portobello Mushroom

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 and a glass of cab sauv.

Recipe and photo courtesy of Sarah from Kiwi & Bean.

Prep Time: 30 mins. | Cook Time: 10 mins. | Serves:  4
Tip:  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.


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.