Caponata (Sweet and sour eggplant stew)

Ingredients

• 2 medium-large eggplants
• 2/3 cup olive oil + 2 tablespoons
• 1 small onion, finely diced
• 2 celery sticks, diced
• 1.5 cups (380g) tomato passata
• 1/4 cup of capers
• 1/2 cup pitted olives
• 2 tablespoons vinegar
• 1 tablespoon sugar
• 3 tablespoons pine nuts
• 1/2 teaspoon salt
• handful of basil leaves, optional