How to Make It
Quarter the eggplant lengthwise. Scoop out the very seedy parts and discard. Cut the remaining eggplant into 1/2-inch dice. In a colander set in the sink, lightly salt the eggplant cubes and toss well. Top with a sturdy plate weighed down with a heavy can and let drain for 1 hour. Rinse the eggplant cubes and pat dry.
In a large skillet, heat 1 tablespoon of the oil. Add the eggplant and cook over moderately high heat, stirring occasionally, until tender, about 5 minutes. Transfer the eggplant to a bowl.
Add the onion and the remaining 2 tablespoons of oil to the skillet and cook over moderately low heat until the onion is tender, about 6 minutes. Return the eggplant to the skillet. Stir in the capers, olives and balsamic vinegar and cook until the vinegar has evaporated. Add the tomato sauce and cook over low heat, stirring, until thickened, about 2 minutes. Season with salt and pepper and transfer to a bowl to cool.
Shortly before serving, spread the caponata on the baguette toasts and garnish with the basil.