Preheat the oven to 190ºC. Place the vine tomatoes in a shallow roasting dish and drizzle over the olive oil and balsamic vinegar. Sprinkle over the brown sugar and seasoning.
Roast the tomatoes in the preheated oven for 15-20 minutes until they are starting to burst and the juices are caramelising. Remove the tomatoes from the oven and set aside a few small bunches to use as a garnish.
Remove the remaining tomatoes from the vines and reserve any juices. Remove the cores from the tomatoes and roughly chop the flesh.
In a large saucepan, heat the butter over a medium heat and sauté the onion, garlic and thyme leaves for 3-4 minutes until softened and fragrant. Add the canned tomatoes, roasted chopped tomatoes, the reserved caramelised juices and tomato paste.
Simmer for 20 minutes. Purée the mixture in a food processor or with a stick blender until it is smooth. Adjust the seasoning to taste.
Serve the soup with a swirl of cream, thyme leaves and freshly ground black pepper and a side garnish of the reserved roasted vine tomatoes.