As alfresco eating season gets under way, why not enjoy an array of delicious flavours in a bun? No meat required!

Start with the caramelised onions, as they take the longest to prepare. Peel and chop 2 onions and put them in a cold saucepan. Add 2tbsp butter and put the saucepan on a medium heat. The onions will soon start to release liquid, and the flavours will be concentrated as a result of cooking in their own juices. Stir with a wooden spoon about every 5 mins for 30-40 mins, and check that they’re not burning. If you notice they’re starting to get dry you can add the vinegar earlier. Pour 1tbsp red wine vinegar into the saucepan of onions, raise the heat and considerably reduce without a lid. Put to one side.

Preheat the oven to 180°C. Cut 2 aubergines lengthways into thin slices, ideally by using a mandoline. Pour plenty of oil into a frying pan and heat until it starts to smoke. Fry the slices of aubergine on both sides so they take on a nice colour, then transfer them to paper towels so they release the excess fat.

Lay 3-4 slices of aubergine in a row so they form a long strip. Repeat with the remaining slices of aubergine so you get 6 long strips. Take 200g tomato purèe and spread a thin layer on each strip, then sprinkle 250g grated mozzarella and 100g grated Parmesan on top. Roll each length up to form a round – as if making a cinnamon roll – of about the same diameter as the bun. Transfer the aubergine rolls to ramekins or heat-resistant teacups. Put in the oven and bake for about 20 mins.

These aubergine patties work best if they are given time to settle, so, once baked allow them to cool in the fridge for an hour or so, then reheat them in an oven at 175°C for 10 mins until warmed through. Butter the buns on the cut surface and fry them quickly in a frying pan or grill.

Slide a small knife around the edges of the ramekins or teacups to loosen, turn them over and slide the aubergine patties out onto
a large plate. Carefully place a patty on each bun and top with pickled gherkins, caramelised onion and a good dollop of ketchup.

homemade tomato ketchup

Green Burgers by Martin Nordin (£15, Hardie Grant) Photography © Martin Nordin