At the Italian Cooking School, Mamma Corleone in Palermo, Sicily we learned to cook this very tasty dish which can be served hot or cold. It's especially great on fresh bread. It keeps in the fridge for days (unless scoffed first).
The first step in this recipe, which is not absolutely necessary but a good idea, especially for larger, more mature eggplant, is to remove the excess liquid from the eggplant by sprinkling the eggplant cubes with salt and placing them in a colander, with a small plate on top to exert some gentle pressure and one below to catch the eggplant liquid as it drains. Let the eggplant steep for an hour or more.
We don't usually bother with this step and the result is still really yummy.
When you are ready to cook, gather up a handful of eggplant with a paper towel, give it a gentle squeeze to dry the cubes, and fry them in abundant olive oil. Work in batches if necessary to avoid crowding the eggplant, removing them with a skimmer when the eggplant cubes are just lightly browned to a basket or bowl lined with paper towels to soak up the excess oil.
When all your eggplant is done, there should be less oil in the pan, but still enough to cook with. Add the celery, sauté for a few minutes until the celery is tender but still has some ‘bite’ left in it. Season with salt and pepper as it cooks. Remove with a skimmer and set aside.
Now add the onion to the remaining oil in the pot and sauté it gently until it is quite soft. Add the tomato. Simmer the tomato until it has melted and reduced to a nice, sauce-like consistency.
Now add back your eggplant and celery, along with the capers, pignoli, olives. Allow everything to simmer together for about10 minutes. A minute or two before it’s done, add the sugar and vinegar, mix well (but gently!), taste and adjust with more sugar or vinegar if necessary. Turn off the heat and let the dish cool entirely before serving.