cut the tomatoes in half and place cut side up on a large sheet of aluminium foil. sprinkle each tomato with the garlic and drizzle with olive oil and balsamic vinegar, sprinkle a little sugar on each one and loosely wrap in the foil. Place on a barbecue for around 30 minutes. Alternatively, place in a tray and cook in an oven at 200C for 30 minutes.