Preheat the oven to 250C. Arrange the vegetables in a large roasting tin with a little space around them, with the garlic bulbs in the centre (if the vegetables don't fit  in one tin, use two and cook separately). Drizzle the vegetables with olive oil, sprinkle with fine sea salt and cook for 35 minutes, turning every 15 minutes or so, until the skins are blackened and the vegetables are very tender. The idea is to get as much colour and smoky flavor without burning the flesh.

When cooked, remove the tin from the oven, let it cool slightly and cover tightly with plastic wrap. Set aside until vegetables are cool enough to handle.

Remove the outer layer of the leek and discard. Cut the rest of the leek diagonally into 2-centimetre-wide strips. Carefully remove and discard the skin of the eggplant. Strip off the flesh into 1-centimetre-wide strips following the length of the eggplant.

Cut the end off each garlic bulb, about 1 centimetre from the top, then carefully squeeze out the garlic. Peel and discard the skin from the capsicums. Remove and discard the stalk, seeds and membrane and cut the flesh into 1-centimetre-wide strips. Reserve 1 tablespoon of the cooking juices from the tin.

Place the vegetables in neat, alternating strips on a serving plate. Place the garlic in a small bowl and mash with a spoon, add the cooking juice, sherry vinegar and extra-virgin olive oil and stir well. Pour the dressing over the vegetables and sprinkle with sea-salt flakes.