Maitake Smash Burgers with Sumac Onions

Maitake Smash Burgers with Sumac Onions and Mint Aioli
Jump to Recipe

Smash burgers are having a moment. They seem to be served on every corner of every metropolis. They have been turned into everything from tacos to salads. Smash burgers are even served fries-supreme-style over their traditional side. We have reached peak smash burger and I for one am happy to see it. Burgers, smashed or otherwise, are a perfect food. But why would I present you with a classic burger when I already have one on this site? So instead here is my vegetarian take on the smash burger. These Maitake Smash Burgers feature maitake mushrooms marinated in ras el hanout and olive oil smashed and roasted between two large baking sheets. The mushrooms are piled onto a bun slathered with a mint aioli and topped with sumac onions and fresh cucumber. It may not be your classic burger stand burger but it’s still mighty fine,  so let’s make it!

Maitake mushroom on a cutting board.

We’re going to start by mincing a couple of cloves of garlic. Transfer the garlic to a comically large bowl. I, like most people, have a mental block when it comes to using large pots, pans, bowls, etc. I guess it’s because I think they are more cumbersome to clean or they take up too much dishwasher real estate. So trust me that when I tell you to reach for a large anything it’s because there is no workaround or alternative. So have faith and put that smidgeon of garlic inside a gigantic bowl. 

Sliced maitake mushroom on a cutting board.

With the dishware successfully over-explained, let’s move along by adding to this marinade. That is what we’re making, by the way. This will be a marinade for the maitake mushrooms, but right now it is a whisper of garlic in a cavernous bowl. Let’s remedy that by adding the zest of one lemon. Zest is great when you want the suggestion of citrus without too much acid. Next, add a heaping tablespoon of ras el hanout followed by a little salt and a whole lot of olive oil. Whisk everything together and set the marinade aside.

Mint leaves on a cutting board.

For those of you who are unfamiliar with ras el hanout, allow me to introduce you. Ras el hanout is a medley of spices that pops up in Tunisian, Algerian, and Moroccan cuisines. The name means “head of the shop” in Arabic and it implies that this blend is made up of the highest quality and most valuable spices the seller has to offer. 

Tossing red onion slices in salt and sumac in a bowl.

The spices found in ras el hanout vary from blend to blend. Some shops, companies, and even families guard their ras el hanot ingredients and ratios carefully. But most blends include cardamom, cumin, clove, cinnamon, nutmeg, allspice, ginger, chili, paprika, fenugreek, and turmeric. This is the brand I used. So yeah, ras el hanot has a lot going on and it covers a lot of bases. Not bad for a single ingredient. You can use it as part of a rub for meat, poultry, or fish. Or you can stir it into couscous, pasta, or rice. But today, this particular ras el hanout is bound for a mushroom marinade.

Marinated mushroom slices on a baking sheet.

Now, let’s put the maitake in these Maitake Smash Burgers. I was lucky enough to find this huge maitake mushroom at St. Lawerence market here in Toronto. But if you can only find more rationally sized shrooms, don’t fret. Just stock up on a few little ones and you’ll make up the difference. They might be easier to slice than this bad boy was.

Slice your mushrooms into 1/4-inch slices. Place the mushrooms in the marinade and toss to coat. Transfer to the fridge and chill for 30 minutes. Small pieces may fly off while you’re slicing the mushroom or tossing the slices in their marinade. Do not worry about that. Those little bits will turn into crispy bits after a brief turn in the oven. They add excellent texture and they turned out to be my favourite part of the sandwich. Go figure. 

Mint leaves in a food processor cup.

 While the mushrooms are marinating, we will tackle the sumac onions because they need to hang out for a bit as well. Start by thinly slicing one red onion. You can do this with either a sharp chef’s knife or a mandolin. Pile the onion slices into a bowl and add a heaping teaspoon of sumac and half a teaspoon of salt. Give everything a toss, so the onion slices are evenly coated. Add olive oil and some white wine vinegar and toss to coat once again. Set the onions aside to soften and deepen in flavor. This is also a good time to start preheating your oven to 450°F. 

Smashed maitake mushrooms on a plate.

Now, let’s get the aioli going. This is by far the easiest portion of the recipe. Why? Because all you have to do is pop everything into a blender and let it do the work. So place fresh mint leaves, a minced clove of garlic, salt, lemon juice, and two egg yolks in a blender. Add olive oil and blitz until smooth and thickened. This could take a little bit. Pour the finished aioli into a bowl and chill until ready to serve. 

Maitake Smash Burgers with Sumac Onions and Mint Aioli

Okay, let’s get those mushrooms into the oven. Place a silicon mat on a large baking sheet and arrange the mushroom slices in an even layer. Place a second silicone mat on top of the mushrooms and another baking sheet of equal size. Make sure the bottom of the baking sheet is facing down. On top of the top baking sheet place a cast iron skillet. Pop the whole rig into the oven and roast for 10 minutes. Remove the frying pan, the top baking sheet, and the silicone mat. Flip the mushrooms and bake for 5 minutes more. 

Maitake Smash Burgers with Sumac Onions and Mint Aioli

All that remains is to build your Maitake Smash Burgers. So slather a bun with mint aioli and add some sumac onions. Top the onions with a few mushroom slices and top them with cucumber and more sumac onions. Place the top bun on, well, top, and serve immediately.

And that’s everything you need to know about these Maitake Smash Burgers. Loaded with sharp, tangy, and meaty flavors, this meatless wonder will delight you as much (if not more) as a classic smash burger. 


Maitake Smash Burgers with Sumac Onions and Mint Aioli

Maitake Smash Burgers with Sumac Onions and Mint Aioli

These Maitake Smash Burgers feature marinated maitake mushrooms topped with sumac onions and cucumber slices served on a toasted roll slathered with mint aioli.
Prep Time 28 minutes
Cook Time 15 minutes
Marinating Time 30 minutes
Course Main Course
Servings 4


  • 2 Large Baking Sheets
  • 2 silicone baking mats
  • 1 Large Cast Iron Skillet
  • 1 Food processor or blender


Smashed Maitake Mushrooms

  • 2 cloves garlic minced
  • 1 lemon zested
  • ½ cup olive oil
  • 1 tbsp ras el hanout
  • 1 tsp salt
  • 1-2 large maitake mushrooms** sliced into ¼-inch slices

Sumac Onions

  • 1 red onion thinly sliced
  • tsps sumac
  • ½ tsp salt
  • 2 tbsp olive oil
  • 2 tbsp white wine vinegar

Mint Aioli

  • 28g (1 oz) fresh mint
  • 2 cloves garlic minced
  • 2 egg yolks
  • ½ cup olive oil
  • ½ lemon juiced
  • ¼ tsp salt

Maitake Smash Burgers

  • 4 kaiser rolls toasted
  • 1 batch Mint Aioli see above
  • 1 batch Sumac Onions see above
  • 1 batch Smashed Maitake Mushrooms see above
  • ¼ English cucumber thinly sliced


  • Place the garlic, lemon zest, olive oil, ras el hanout, and salt in a bowl. Whisk to combine and add the mushroom slices. Toss to coat and transfer to the fridge. Let marinate for 30 minutes.
    2 cloves garlic, 1 lemon, ½ cup olive oil, 1 tbsp ras el hanout, 1 tsp salt, 1-2 large maitake mushrooms**
  • While the mushrooms are marinating, preheat the oven to 450°F and make the sumac onions and aioli.
  • Place the onion slices in a large bowl and add the salt and sumac. Toss to coat. Pour in the olive oil and vinegar and stir. Set the onions aside to marinate at room temperature. They should be ready by the time you're ready to serve.
    1 red onion, 1½ tsps sumac, ½ tsp salt, 2 tbsp olive oil, 2 tbsp white wine vinegar
  • Place the mint leaves, garlic, egg yolks, olive oil, lemon juice, and salt in a food processor. Blitz until very smooth. Transfer the aioli to a bowl and place it in the fridge. Chill until ready to serve.
    28g (1 oz) fresh mint, 2 cloves garlic, 2 egg yolks, ½ cup olive oil, ½ lemon, ¼ tsp salt
  • Arrange the marinated mushroom slices on a large baking sheet lined with a silicone baking mat. Place another baking mat on top of the mushrooms and place another baking sheet on top of that. The baking sheet should be the same size and the bottom should be facing down. Place a cast-iron skillet on top of the second baking sheet.
  • Place everything in the oven and roast for 10 minutes. Remove the skillet, the second baking sheet, and the second silicone mat. Flip the mushrooms and roast for 5 more minutes.
  • Slather the Kaiser rolls with the mint aioli and add a layer of sumac onions. Place two mushroom slices on top of the onions and add a layer of cucumber slices followed by another spoonful of the onions. Place the top bun on top and serve immediately.
    4 kaiser rolls, 1 batch Mint Aioli, 1 batch Sumac Onions, 1 batch Smashed Maitake Mushrooms, ¼ English cucumber


** If you can’t find maitake mushrooms as large as the one in the photo, you may have to buy 3-4 smaller ones to make four burgers.
Keyword aiol, maitake, mint, ras el hanout, red onion, sumac

You may also like