Trim the green tops off the aubergines. Halve the aubergines and slice them into fingers around 2cm-thick. Chop those into bite-size chunks.
Warm a casserole dish over a medium heat for 2 mins, then add 2 tbsp oil and the aubergines. Fry for 8-10 mins, turning once or twice, till the aubergine chunks are browned all over.
While the aubergines fry, halve, peel and finely chop the red onions. Chop the courgettes into chunks that match the aubergines. Trim the dry ends off the celery sticks and finely slice them.
Lift the aubergine out of the pan and pop it on a plate. Add another 1 tbsp oil to the pan and tip in the chopped onions, courgettes and celery. Season with a pinch of salt and pepper. Cover. Gently fry for 10 mins, stirring often, till the veg have softened.
While the veg fry, scrub the potatoes and slice them into 1cm-thick rounds. Peel and crush the garlic. Finely chop the parsley stalks, keeping the leaves for later.
Tip the aubergine back into the pan. Add the potatoes, garlic and parsley stalks. Measure out 1 tsp dried oregano and add that with a pinch of dried chilli flakes. They’re spicy, so add as much or as little as you like.
S tir in 1 tbsp caster sugar and 2 tbsp red wine vinegar. Pour in the passata. Add 500ml boiling water. Give everything a good stir to mix, then pop on a lid. Turn up the heat and bring to the boil. Once it’s boiling, turn the heat down and simmer for 30 mins. While the veg simmer, roughly chop the parsley leaves.
T he potatoes should be tender and starting to collapse. Taste the stew and add more salt, pepper or chilli flakes if you think it needs it. Ladle the stew into warm bowls and garnish with the chopped parsley leaves to serve.