Grilled Portobello Burgers with Piquillo Aioli

Here is a recipe that has been sitting, waiting patiently in my Epicurious recipe box for over a year, along with 419 friends.  Why, oh why have we only just met, in my 27th year of life?  I think you made me nervous.  I just knew I’d love you, but I wasn’t so sure about my live-in burger-connoisseur,  Mr. Medium-Rare.

All the portobello sandwiches and burgers I have ever had have been lifeless.  Limp.  Slightly cold.  Lacking savoriness.  Sometimes slathered in bland marinara, sometimes paired with other grilled but cold zucchini or red bell pepper and topped with a cold disc of mozzarella.  Just thinking about it makes me feel glum.

Such sandwiches are never rubbed with thyme and garlic and left to marinate…or grilled until seared on the outside, firm and juicy on the inside.  Not topped with a melted dome of smoked gouda that imparts the smokiness that normally only non-vegetarian burgers possess.  No watercress or other fresh greens to add a contrast in temperature, texture or color…oh, and you can just forget about aioli–especially one with piquillo peppers and garlic, dotted with fresh thyme.  One last note:  those lifeless portobellos never sit upon toasty sourdough rolls.

I’m sorry for stereo-typing you, grilled portobello burger.  I was wrong about you.  Let’s be friends.

Grilled Portobello Burgers with Piquillo Aioli

Adapted with just a few tweaks from Bon Appetit,  July 2008


  • 1/2 cup chopped drained piquillo peppers from a jar, (or roasted red peppers in a pinch)
  • 1 tablespoon red wine vinegar
  • 2 teaspoons finely chopped fresh thyme leaves
  • 1 garlic clove, minced
  • 1/2 cup mayonnaise
  • ground cayenne to taste
  • salt to taste

If making the aioli from scratch (ie: homemade mayonnaise), you will need the following…

  • 1 egg yolk, preferably organic
  • 1/4 cup olive oil
  • 1/4 cup grapeseed or canola oil
  • 1/8 tsp salt, or to taste

Portobello Burgers:

  • 6 large portobello mushrooms; washed, stems removed, gills scraped out with a spoon
  • 1 sweet onion, cut into 1/3 inch slices
  • 2 teaspoons chopped fresh thyme leaves
  • 2 garlic cloves, minced
  • 6 slices smoked gouda
  • 6 sourdough or ciabatta rolls
  • 1 bunch watercress, stems trimmed, or a handful of  mixed greens

For the aioli (from scratch):

Whisk the egg yolks and salt together in a small bowl, then pour into a food processor.  Add the minced garlic, piquillo peppers, thyme and vinegar.  Blend for about 30 seconds until pureed.  With the food processor continuously running, pour in the grapeseed oil (or canola oil) followed by the olive oil in a slow and steady stream.

Remove from the food processor and season to taste with salt, cayenne, and black pepper.  Chill until ready to serve. This aioli can be made up to 3 days in advance if refrigerated immediately.

For the aioli (if using prepared mayonnaise):

Combine the piquillo peppers, garlic, thyme, and red wine vinegar in a food processor and blend until pureed.  Add the mayonnaise and pulse for about 3 seconds to combine.  Remove the mixture to a small bowl and season to taste with salt, black pepper, and cayenne.  Chill until ready to serve.

For the mushrooms and onions:

Arrange the portobellos on a baking sheet.  Brush both sides with oil.  Rub each side with minced garlic, thyme, salt and pepper.  Allow mushrooms to sit, gill side up for at least 30 minutes and up to 2 hours.  Lightly brush the onions with oil and sprinkle with salt.


Lightly oil the grates of a grill or grill pan and pre-heat over medium-high heat.  Place the onions and mushrooms on the rack, and cook until grill marks appear, about 4 minutes.  Flip and cook another 6-8 minutes, or until mushrooms are tender and striped with grill marks.  Place 1 slice of gouda on top of each mushroom, and cook until gouda is melted, about 1 minute.  Slice each sourdough roll in half and place on the grill until toasted.

Build your Burger:

Spread aioli on the cut side of each roll.  Top each roll with a mushroom, grilled onions and watercress.  Serve immediately while hot.





Filed under Main Dishes, Sandwiches and Burgers

6 responses to “Grilled Portobello Burgers with Piquillo Aioli

  1. Karissa

    I just made these and I can’t wait to share them with N!

  2. whitney

    We made this last night! Yummmm! The spice of the watercress is so perfect with the bold flavors of the onion and the aioli. It was delicious. But I’m sure you knew all this already 😉

  3. Auntie Karen

    Happy Happy Birthday dear Jenny!! I am going to buy some ‘bellos today. My Mr. Medium-Well (ick) won’t eat ‘shrooms…..oh what he is missing. However, Mrs. Medium-Rare loves everything! This is an amazing recipe & I look forward to your cooking challenges in my inbox more than I can tell you. Keeping you in my prayers & thoughts daily sweetie! Enjoy this day & your year ahead! Love you!

    • Thanks for the birthday wishes! As for the portobellos, Mr. Medium Rare is missing out big time. I’m glad you are making them for yourself, though. I hope you enjoy spending more time in the kitchen!

  4. elementonestudio

    seriously, you are amazing. And how are you still so skinny? You are an incredible cook, and writer for that matter. Keep it up, and invite me over!

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