Cut the tomatoes in half and scoop the seeds and pulp into a sieve set over a bowl to collect the juices. Chop the tomato flesh fairly finely.

Heat the butter and the oil in a casserole over a medium heat and cook the onion and garlic for 5 minutes, until softened but not coloured. Add the tomatoes and their juices (throw out the seeds), the ketchup, celery, thyme and tomato juice and season with salt and pepper. Bring to the boil, then lower the heat and simmer for 20-30 minutes, until it has reduced by about two-thirds.

Pick out the pieces of celery and thyme, add the cream and blitz the soup in a blender until smooth. Pass the soup through a fine sieve into the cleaned pan, bring back up to a simmer and serve.