With the BBQ season approaching, it is time for a plant-powered burger to come into its own – although I have to admit that this one is cooked in the oven as the mushrooms dry out too much on a fierce grill!
Portabello mushrooms are available in different sizes, from barely 4 cm/1 1/2 inches across to giant specimens which can weigh almost half a pound. They are simply an adult brown mushroom and acquire not only bulk but depth of flavour as they grow to maturity. Their firm, meaty texture makes them an excellent choice for stuffing and for stewing, and in this recipe, they provide a welcome chewiness. They do tend to shrink quite considerably as they cook, so choose the largest ones you can find – or if there are only small ones on offer, allow three or four per burger and adjust the cooking time accordingly. Peeling the mushrooms exposes the white, porous flesh of the cap, which enables it to absorb moisture and flavour.
I love these burgers with a vegan mustard “mayonnaise” to add an extra layer of flavour but feel free to use any of your favourite accompaniments.
Serves 2
For the burgers:-
1 small red and 1 small yellow pepper, about 150 g/5 oz each, cut into 1 cm strips
175 g/6 oz red onions, peeled and thickly sliced
45 ml/3 tbsp olive oil
2 big fat portabello mushrooms, peeled
1 sprig fresh rosemary, needles finely chopped
2 hamburger buns
Fine sea salt and freshly ground black pepper
For the mustard “mayonnaise”:-
100 g/4 oz raw cashew nuts
15 ml/1 tbsp smooth Dijon mustard or to taste
2.5 ml/1/2 tsp wholegrain mustard
5 ml/1 tsp bouillon powder
1 garlic clove, peeled
45 ml/3 tbsp olive oil
Fresh lemon juice
Fine sea salt and freshly ground black pepper
For the mayonnaise, blend the nuts, mustards, bouillon powder, garlic, olive oil and 1 tbsp of lemon juice in a small food processor until very smooth. Check the seasoning and add a bit more lemon juice if the flavour needs brightening. Set aside while you prepare the mushrooms, or refrigerate if it is more convenient but the flavour does tend to intensify with time.
Preheat the oven to 200oC/400oF/gas 6/fan oven 180oC.
Toss the peppers and onions together in a baking dish with 1 tbsp of olive oil and some seasoning. Bake on the top shelf, stirring occasionally, until soft and just starting blacken along the edges, about 30 minutes. Stir in the rosemary and keep warm (or reheat when you are ready).
Place the mushrooms gill side up in a baking dish where they fit snugly. Season, drizzle with 1 tbsp of olive oil and bake in the oven on the shelf below the peppers until soft and cooked through, 30 to 40 minutes.
Split the buns and toast the cut side. Place the bottom halves on 2 warm plates and top with a mushroom. Spoon the peppers and onions over it and drizzle with the remaining 1 tbsp of olive oil. Slather with the mustard mayonnaise.
Serve immediately.