In Dinner, Lunch, Recipes

Hamburgers in Portobello Buns with Sautéed Onions

Hamburgers in Portobello Buns with Sautéed Onions

Nothing beats mixing your own hamburgers! And if you have a large crowd to please, they are easy to prepare and incredibly delicious, you’ll never look back!
Prep Time 30 minutes
Cook Time 20 minutes
Total Time 50 minutes
Servings 10 Hamburgers


  • 2 lbs beef mince meat
  • 1 egg
  • 4/5 tbsp chestnut flour Gluten-free
  • 1 tbsp. cold water
  • 1 tbsp ketchup
  • 1 tsp tamari sauce
  • 1 onion large finely chopped (use a mini chopper if you have)
  • sea salt & white pepper
  • white pepper

Sautéed Onions

  • 2 onions finely sliced
  • 2 tbsp rapeseed oil
  • sea salt
  • garlic granules optional
  • paprika optional

Serving Suggestion (optional) If you would like to serve the hamburger in Portobello Mushrooms, instead a bugger bun

  • 20 portobello mushrooms remove gills
  • 4 tbsp olive oil
  • sea salt
  • 5 avocadoes
  • 6 salad tomatoes thinly sliced
  • 2 red onions thinly sliced
  • 2 romaine lettuce core removed, halved


  • Pre-heat the oven to 400°F, gas mark 6, 200°C (180°C fan-assisted).
  • In a magimix chop one large onion, then place in your mixing bowl. Then add 1 tbsp. of cold water to the finely chopped onion to form a paste, then season with the salt & pepper, ketchup and tamari sauce.
  • Then slowly mix in the mince meat ½ a packet at a time, with a wooden spoon or use your hand (using your hand is best).
  • Then make a well in the centre of the mix and add your egg, beat with the wooden spoon until the egg is nicely combined into the mixture. Then slowly incorporate the chestnut flour (gluten-free), continue to mix well until everything is binded together.
  • You can make this mixture the night before using and leave covered in the fridge, this actually helps to shape the burgers, as the mixture will get firmer overnight.
  • To make the burger collect a large handful of the mixture, and then roll into a ball in the palm of your hands, then place on the pre-lined tray and slightly flatten.
  • Line two baking trays with parchment paper or silicone baking mats. On one tray add the shaped burgers. And on the other tray add the mushrooms, cap side facing down, brush the mushrooms with olive oil and season with sea salt and cracked pepper. Bake everything in the oven for 20 minutes (if you like your burgers slightly pink, reduce cooking time by 5 minutes for the burgers).
  • To make the sautéed onions, place a large non-stick frying pan on the stove add the rapeseed oil together with the sliced onions, cook over a medium heat for 5 minutes, then season with sea salt, white pepper and a little garlic granules and paprika. Continue to cook for a further 5 minutes, until soft over a gentle heat, continue stirring throughout the cooking process.
  • When the burgers have cooked, allow to rest for 5 minutes, them assemble and serve with the soft onions.


LISA’S TIP - I love to serve these burgers in Portobello mushroom caps with cos or romaine lettuce, a few slices of tomato and honey mustard! Alternatively you can serve in a bun or with some potato wedges. You can also make a batch of burger and then keep them in the fridge, and chop them up and add to a salad.
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