Preheat oven to 200°C and line a baking tray with paper.
Place tomatoes onto paper and sprinkle with salt, 2 tbsp of the sugar, balsamic vinegar and EVOO.
Roast 15 minutes and switch oven off. Leave tomatoes in oven until cooled.
Meanwhile place a little more EVOO, onions and garlic into Thermomix bowl and chop 4 sec/speed 6.
Sauté 10 min/100°C/speed 1.
Add diced tinned tomatoes and roasted tomatoes. Cook 10 min/100°C/speed 1.
Puree 10 sec/speed 6. Adjust seasoning with salt, pepper, balsamic vinegar and sugar to taste.
Serve hot with a dollop of sour cream.