Portobello ‘Steak’ Burger with Cheddar, Rocket and Mustard
Why this recipe works
- Deep savoury flavour: Balsamic vinegar brings tang while soy sauce adds umami, helping the portobello taste rich and well seasoned.
- Balanced texture: The tender mushroom, melted Cheddar, crisp toasted bun and peppery rocket give the burger enough contrast to feel complete.
- Fast to cook: A short marinade and a single frying pan keep the recipe straightforward enough for a quick vegetarian dinner.
Get the most out of this recipe
Ingredient notes
- Choose firm portobellos: Look for mushrooms that feel firm and dry rather than damp or collapsing, as they sear better and hold their shape in the bun.
- Use mature Cheddar: A stronger Cheddar stands up to the balsamic-soy marinade and gives the burger a fuller, more savoury finish.
- Wipe, don’t soak: Clean the mushrooms with a damp cloth or paper towel so they do not absorb excess water before searing.
Texture tips
- Keep the mushrooms juicy: Avoid pressing down on the mushrooms while they sear; letting them brown undisturbed helps keep the juices inside.
- Toast the buns well: Toasting the cut sides in the pan helps them stand up to the mushroom juices and melted cheese.
- Melt the cheese gently: Lower the heat once the Cheddar is added so the cheese melts without driving too much moisture out of the mushroom.
Ingredient swaps
- Swap the cheese: Gruyere works well in place of Cheddar if you want a nuttier, smoother melt.
- Change the vinegar: Sherry vinegar can replace balsamic vinegar for a sharper, drier tang.
- Use another peppery green: Watercress is a good alternative to rocket and brings a similarly sharp bite.
Make-ahead tips
- Store components separately: Keep cooked mushrooms and cheese apart from the buns and rocket so the burger does not become soggy.
- Reheat before assembling: Warm the mushrooms in a frying pan over medium heat until piping hot, then build the burger just before serving.
- Assemble fresh: For the best texture, toast the buns and add the mustard, rocket and mushroom only when ready to eat.
Equipment you'll need
Ingredients
Instructions
- Wipe the mushrooms clean and remove the stems. In a mixing bowl, whisk together the balsamic vinegar, soy sauce and 1 tbsp of the olive oil. Add the mushrooms and turn to coat, then leave for 10 minutes, spooning the marinade over once or twice.
- Heat a large frying pan over medium-high heat and add the remaining olive oil. Lift the mushrooms from the marinade (keep the marinade) and sear cap-side down for 3 to 4 minutes until well browned, then flip. Pour in the reserved marinade and cook for 3 to 4 minutes more, basting, until the mushrooms are tender and glossy.
- Reduce the heat to low and lay the Cheddar cheese over the mushrooms; cover the pan and let it melt for 1 to 2 minutes. Transfer the mushrooms to a plate and keep warm.
- Toast the brioche buns cut-side down in the same pan for 30 to 60 seconds until golden. Spread English mustard over the bun bases, add a cheesy mushroom to each, then top with rocket and the bun lids. Serve straight away.
Recipe notes
Tips
- For the juiciest result, avoid pressing down on the mushrooms while they sear; let them brown undisturbed, then baste with the pan juices.
- If you are serving anyone vulnerable to foodborne illness, make sure the mushrooms are cooked until piping hot all the way through.
Substitutions
- Replace Cheddar cheese with Gruyere cheese for a nuttier melt.
- Replace balsamic vinegar with sherry vinegar for a sharper, drier tang.
- Replace rocket with watercress for a similarly peppery bite.
Storage
- Refrigerate up to 2 days
- Store cooked mushrooms and cheese separately from the buns and rocket in an airtight container. Reheat the mushrooms in a frying pan over medium heat for 2 to 3 minutes until piping hot, then assemble fresh.
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Recipe overview
- Servings: 2 servings
- Total time: 25min (20min active)
- Difficulty: Easy
- Cuisine: British
-
Allergens:
Gluten Milk Soybeans Wheat
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