Agrodolce -- sour-sweet -- is the whole point of this dish, and it is astonishingly easy to get wrong in either direction. Too much vinegar and it tastes like a mistake; too much sugar and it tastes like dessert that wandered onto the wrong plate. My aunt makes the only version in this family anyone fully trusts, and she has never once written down her exact measurements, which I've chosen to interpret as a challenge rather than a dead end.
Serves 6 as a side, or 4 as a light main with crusty bread.
Salt the eggplant cubes, and let them sit in a colander for thirty minutes. Pat dry, then fry in batches in a generous amount of olive oil until golden and tender. Drain on paper towels, and set aside.
In the same pan, with a little fresh oil if needed, cook the celery until just tender-crisp, about five minutes, and set it aside separately -- it's added back at the end specifically so it keeps some bite, rather than going soft along with everything else. Cook the onion in the same pan until soft.
Add the crushed tomatoes to the onion, and simmer for ten minutes. Stir in the olives, capers, pine nuts, and raisins, and cook for a few minutes more.
Stir the vinegar and sugar together in a small bowl until the sugar dissolves, then add this to the pan. Simmer for five minutes, tasting as you go -- you're after a balance where neither the sweet nor the sour announces itself over the other, not a fight between the two. Adjust with a little more of either if it leans too far one way.
Fold in the fried eggplant and the reserved celery. Remove from the heat, stir in the basil and parsley, and let it cool to room temperature before serving. If you have the patience, cover it and refrigerate overnight instead -- caponata left to rest genuinely tastes better the next day, once the sweet and sour flavors have had time to settle into each other rather than sitting separately.
If the dish tastes sharply of vinegar rather than balanced, it needed more sugar to meet it, or wasn't simmered long enough afterward for the two to properly marry. If it tastes cloying instead, the opposite is true; add a little more vinegar, a splash at a time, tasting after each addition. If the eggplant turns to mush, it fried too long, or in oil that wasn't hot enough to seal it quickly. And if the celery has gone limp and indistinguishable from everything else, it was added back too early instead of at the very end, where its crunch is meant to survive.