Heat oven to 170C/150C fan/gas 3 - 4. Bring a pan of water to the boil and get a bowl of iced water at the ready. Cut a small slit in the bottom of each tomato then plunge into boiling water in batches for 10 secs then lift out into the iced water.
Drain and peel the tomatoes then halve and place on a baking tray cut side up. Sprinkle with salt, pepper and the sugar. Drizzle with the vinegar and 1 tbsp of the olive oil. Roast the tomatoes for 1hr until semi-dried and set aside.
Heat the remaining oil in a large saucepan and cook the celery and carrot gently for about 10 mins until very soft. Add the tied herbs and garlic infused oil and cook for a minute more. Stir in the tomato purée then tip in the roasted tomatoes and any juices from the tray. Pour over the stock and season with salt and pepper. Bring to the boil then turn the heat down and simmer for 10 mins.
Remove the tied herbs and discard. Add the lactose free cream then take off the heat, blitz well with a hand blender. If you want a smoother soup then it can be sieved but this isn’t really necessary. The soup can now be cooled and kept for 3 days in the fridge or frozen for up to 1 month. For a dinner party, serve the soup with a sprig of thyme and a drizzle of good quality olive oil.