Warm ½ cup of the olive oil in a large skillet pan on medium high heat. Add eggplant and cook until lightly brown, but still firm, about 5 minutes. Set aside in a a flameproof casserole or deep sauce pan.
Warm the 2 tablespoons of olive oil in the skillet and add the onions. Cook until wilted, about 4 minutes. Stir in celery, then tomatoes. Crush the tomatoes with the back of a slotted spoon. Simmer over medium low heat until the tomatoes begin to sweeten, but celery is still crisp, about 15 minutes. Stir in capers and pine nuts. Transfer this into the casserole pan with the eggplant.
In a small sauce pan on low heat, stir together sugar and vinegar. Warm until it dissolves. Stir into the eggplant mixture. Season with salt and pepper.
Cover and simmer over low heat, stirring frequently until tomatoes are cooked and the vegetables are tender but not mushy-about 15-20 minutes.
Store in refrigerator. Keeps for a week or a little more. Serve warm, room temperature, or chilled. Delicious on Italian country bread or bruschetta!