Trick 1. Roasting tomatoes require roominess
Otherwise, they sweat rather than caramelise.
Trick 2. Roast the tomatoes dry (that is, without any oil)
Again, dry roasted tomatoes sweat less, and as a result they lose more moisture, intensifying their flavours.
Trick 3, adjusted: Season with sea salt, black pepper & sugar
Sprinkle this mixture all over the halved tomatoes and put them in the middle of a 160 C oven.
Once they’re out of the oven, as quickly as humanly possible remove them from their syrupy spots on the tray and crowd them into a dish. This is important because in a matter of half minutes, those syrupy spots will turn to glue, fixing the skins of the tomatoes onto the tray.
Don't forget about the caramelized juices, try gently dissolving them, like you would other roasting juices. Place the pan directly on the stove and with a very little water or stock, gently rub the pan with a wooden spoon until the caramel gives way and dissolves again. Let any excess liquid simmer away and then pour this syrup back onto your tomatoes.
Use the tomatoes straight away, in a salad with lentils, roasted cauliflower and Persian feta, perhaps. Or marinate them overnight. Drizzle them with olive oil, some freshly chopped or torn herbs, maybe a few thin slices of garlic and eat them smashed into your toast tomorrow morning.
Source : Skye Gyngell