The Ultimate Vegan Portobello Mushroom Burger


The ultimate vegan portobello mushroom burger –  two portobello mushrooms stuffed with melty cashew cheese, coated in panko breadcrumbs and fried until crispy then sprinkled with rosemary salt.  

Heyyyy! This is a big recipe today! But so worth it, it’s really the ultimate, that’s not a big lie I promise – It’s so so so very good. That cheese filling. That crunchy crust. Just yes.

Picture this… biting through a soft, fluffy burger bun to reach the crunchiest fried crust that has ever been, a whiff of fragrant rosemary salt, then two juicy and meaty portobello mushrooms. Now you’re hit with the center of melty, fondue-y cheese – ‘could anything be better?’ you think! Then fresh slices of lettuce and tomato, buttery slices of avocado and the tang and spice of the cashew mayo wraps with the cheese and the fried crust and the meaty mushrooms and the fluffy bun and suddenly everything in the world seems okay. And this, you think, is burger heaven. Especially if you’ve made yourself some fat potato or sweet potato chips with rosemary salt and extra spicy mayo to eat alongside. And all of it washed down with an ice. cold. beer.

At least that was my experience. And I really feel like that experience needs to be shared with the world. Or else I’m just being selfish! So without further ado, I give you the ultimate vegan portobello mushroom burger!

5 from 1 vote

The Ultimate Vegan Portobello Mushroom Burger

vegan, egg‐free, dairy‐free, soy‐free, sugar‐free
The ultimate vegan portobello mushroom burger — two portobello mushrooms stuffed with melty cashew cheese, coated in panko breadcrumbs and fried until crispy then sprinkled with rosemary salt. Layered on a toasted burger bun with a spicy cashew mayo, avocado, tomato, lettuce and pickles.
Servings 4


cashew cheese filling

  • 1 cup cashews soaked for 6–8 hours or overnight in cold water or 2–3 hours in just boiled water
  • 1/3 cup coconut milk
  • 1/3 cup water
  • 2 tbsp nutritional yeast
  • 1/2 tsp white miso
  • 1 tbsp coconut oil
  • 1 tbsp lemon juice
  • 2 tbsp arrowroot starch
  • 1/2 tsp dijon mustard
  • 1/4 tsp fine sea salt + more to taste
  • 1/4 tsp garlic powder
  • 1/8 tsp turmeric
  • 1/8 tsp paprika
  • a few cracks black pepper


  • 1 cup cashews soaked for 6–8 hours or overnight in cold water or 2–3 hours in just boiled water
  • 5 tbsp olive oil
  • 1/4 cup water
  • 1 tsp white wine vinegar
  • 1 tbsp ketchup / tomato sauce
  • 1 tsp dijon mustard
  • 4 slices dill pickle
  • 1 tbsp lemon juice
  • 1/4 tsp garlic powder
  • 1/4 tsp hot or smoked paprika
  • 1/8 tsp cayenne pepper
  • 1/4 tsp fine sea salt + more to taste

rosemary salt

  • 2 tbsp flaky sea salt
  • 1 tbsp finely chopped rosemary
  • a few cracks of black pepper


  • 8 large portobello mushrooms stems & gills removed
  • 2 cup flour
  • 2 tbsp finely chopped rosemary
  • 1 1/2 cup almond milk
  • 3 cup panko breadcrumbs
  • peanut oil to fry – enough to fill a large pot halfway with oil about 3 litres


  • 4 burger buns
  • coconut oil to toast the buns
  • sliced tomatoes
  • lettuce leaves washed + torn to burger size
  • a few thin avocado slices per burger
  • dill pickles
  • thick cut baked or fried potato / sweet potato chips sprinkled with extra rosemary salt & served with the leftover cashew mayo – optional but highly recommended!


cashew cheese

  • Drain and rinse the cashews, then place in a blender (preferably high‐speed) with all the other ingredients and blend until completely smooth, creamy and the mix feels warm. The arrowroot should begin to 'activate', making the cheese look like melty cheese fondue. Taste, adjust the seasoning if needed then scrape into a container, cover and place in the fridge to chill. Rinse out the blender ready to use for the mayo.


  • Drain and rinse the cashews and place all the ingredients in a blender. Blend until completely smooth. Try not to over‐blend or the olive oil may become bitter – the mix shouldn't get too hot. Taste and adjust the seasoning if needed, scrape into a container, cover and place in the fridge to chill and thicken.*

rosemary salt

  • In a mortar and pestle, bash together 1 tbsp of the salt, the rosemary and the pepper until mashed together and fragrant (alternatively you can do this in a small food processor). Stir in the remaining 1 tbsp sea salt then scatter on a baking tray and leave to dry at room temp while you make the burgers.*


  • Steam the portobellos in a covered steaming basket, over a pot filled with about 5cm of simmering water. Steam until completely soft, tender and flexible (you may need to do this in two batches), about 10 minutes. When cooked, remove and place between two tea towels. Press down on the towels to help the mushrooms release their liquid. Place the mushrooms on a cooling rack and allow them to dry and cool completely.
  • Take one portobello, top facing down, and place 1/4 cup of the chilled cashew cheese in the middle. Place another portobello on top. Gently press and mould the portobellos together. You can also use a big piece of cling wrap – place under the bottom portobello, gather the ends together and twist – to help mould the portobello's together. Repeat with the other portobello's.
  • Mix the flour and chopped rosemary together and place on a large plate, pour the almond milk into a large bowl, and place the panko on large plate. Coat the portobello's with the flour mix, then the almond milk, then the panko, making sure to cover the sides as well. Repeat this coating process one more time, then allow the coated portobello burger to rest on a piece of baking paper while you repeat this process with the other 3 burgers.
  • Heat your peanut oil to 190°C / 375°F use a deep fry thermometer, then gently place your burgers into the oil (fry two at a time) using a slotted spoon. Move the burgers around as they cook so that they don't sit on the bottom, and so they fry evenly. Cook until golden brown and crispy, about 4 minutes. Transfer to a tea towel lined plate, sprinkle both sides with a little rosemary salt and repeat with the remaining two burgers.


  • Cut your burger buns in half and brush both sides with a little coconut oil. Fry in a medium‐high heat pan or cook under the grill until lightly toasted. Spread the top buns with about 1 tbsp mayo. Place a few thin slices of avo on the bottom buns, then top with the fried mushroom patty, the lettuce, then the tomato (and pickles if using).
  • Serve asap. The best way to serve – with chips tossed with rosemary salt, the leftover spicy mayo for dipping and a cold beer! The ultimate.

The Ultimate Vegan Portobello Mushroom Burger | The Floured Kitchen

The Ultimate Vegan Portobello Mushroom Burger | The Floured Kitchen

The Ultimate Vegan Portobello Mushroom Burger | The Floured Kitchen

These would be amazing to make for a ‘date night’, with beers or big dark chocolate milkshakes, maybe spiked with bourbon. This meal gets big very quickly, so make room. Don’t eat lunch. Or breakfast. Just eat these!

p.s. A few of the elements in this recipe are amazing for other things. The cashew cheese is a seriously addictive fondue-like dip – serve it as an amazing appetiser with bread, crackers and raw seasonal vegetables. The spicy mayo is incredible with chips, on tacos, drizzled over pizza, as a potato salad dressing etc. etc. The rosemary salt can be used to add extra flavour to almost anything – I love using it in autumn and winter to top soups, stews and pastas (and everything else!) for a little hit of flavour, often with a little lemon zest mixed in as well. Let your imagination run wild!

You can sub store‐bought vegan cheese and mayo, and rosemary salt if you’d like to make this recipe far simpler and less daunting 🙂


The Ultimate Vegan Portobello Mushroom Burger | The Floured Kitchen

Join the Conversation

  1. caroline says:

    Wow, this is absolutely gorgeous, creative and delicious looking!!! I will definitely try this!! Great job!

    1. Thanks so much Caroline! Hope you love it if you give it a try 🙂

  2. 5 stars
    Made this tonight but without the cashew cheese filling (no cashews, no time to soak anyway as it was a semi-last minute meal decision) and it was unreal. We also used simple vegan mayo, but even without the ‘ultimate’ add-ons, I’ve never crusted a portobello before. So good! Thanks for sharing!

    1. That’s so good to hear Abby! Cheers for the comment 🙂

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