Eggplant Parmigiana

• 3 tablespoons olive oil, plus extra for brushing
• 1 onion, finely chopped
• 1 garlic clove

Heat 2 tablespoons of the oil in a heavy pan and cook the onion over a medium heat for 10 minutes, or until soft and golden. Add the garlic and cook for 2 minutes more. Stir in the tomato passata, sugar, oregano and salt and pepper. Let the sauce bubble up, then reduce the heat to low. Cover and sim