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1
Slit each aubergine lengthwise along one side, leaving the stem intact. Salt the cut surface and interior generously, place the aubergines in a colander, and press them under a weighted plate for a minimum of 30 minutes. Drain and pat firmly dry with kitchen paper. The flesh will have released a significant quantity of dark liquid; this is the correct result.
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2
Warm a generous film of olive oil in a wide, heavy pan over medium heat. Fry the aubergines, turning, until the skin blisters and the flesh begins to colour at the edges. Remove and set aside. The aubergines should feel slightly softened when pressed but remain structurally intact.
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3
In the same pan, add more olive oil and cook the sliced onions and garlic over low heat for a minimum of 25 minutes, stirring occasionally. This step is where the dish lives or dies: the onions must collapse completely into a deep golden, sweet mass — pale or sharp onions will not sweeten further inside the aubergine and will ruin the filling.
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4
Add the chopped tomatoes and the pinch of sugar to the caramelised onions. Cook over medium-low heat, stirring, until the tomatoes soften and begin to lose their raw acidity but still retain some texture and body. The filling should smell sweet and savoury, not sharp.
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5
Arrange the fried aubergines in a single layer in a wide, lidded braising pan. Open each slit and spoon the onion-tomato filling generously into the cavity. Pour 150–200 ml of olive oil over and around the aubergines so that they are almost poaching in the combined oil and tomato juices. Cover tightly.
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6
Braise over the lowest possible heat until a knife inserted into the thickest part of each aubergine meets zero resistance. Visual colour cues are unreliable here as the aubergines braise covered; the knife test is the sole reliable doneness indicator. The flesh will appear almost translucent at the edges when correctly done.
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7
Remove from the heat. Allow to cool in the pan, uncovered, for a minimum of 30 minutes. The dish is best made a day ahead: refrigerated overnight, the olive oil and tomato juices consolidate into a silky braising liquid. Serve at room temperature, never hot.