1. In a colander set over a large bowl, toss the eggplant with 2 teaspoons kosher salt. Set aside for 1 hour, discard the liquid, then rinse and pat the eggplant dry. Set aside.

2. In a large skillet set over medium heat, combine the olive oil, onion and celery. Cook for 8 minutes, then stir in the garlic and reserved eggplant and cook until browned, about 10 minutes. Add the tomatoes, tomato paste and sugar to the pan and cook for 2 minutes, stirring often, until the tomatoes begin to break down. Stir in the capers, balsamic vinegar and water and season with salt and pepper. Cook over medium-low heat for 20 minutes, stirring frequently, until all the vegetables are tender and the mixture is thick. Season with salt and pepper and set aside to cool. Place in a container with a tight-fitting lid and refrigerate overnight. Sprinkle with the pistachios and serve at room temperature.