Cut the aubergines into quarters and the onions into 8 wedges. Place on a lined baking sheet and drizzle with olive oil. Roast at 180c/170 fan/ gas 5 and roast until soft and golden in colour.
To make the caponata, heat 4 tablespoons of olive oil in a large pan, add the garlic and cook until fragrant. Chop up the cooked aubergine and onions and add to the pan. Add the basil, capers and tomatoes and cook over a medium until thickened. To finish add the balsamic, sweeten with a little agarve. Stir in the cocoa powder and olives – taste and season accordingly. Store in a preserving jar or air-tight container. Keep in the fridge, but take out an hour before serving. Great for up to 5 days.