Starter

Heat olive oil in a large casserole and add onions, celery, carrots, potatoes and bay leaves; fry gently until onions soften (10–15 minutes)
Fill kettle and bring to a boil
Stir in tomato puree, sugar, white vinegar, chopped tomatoes, passata and crumble in the stock cubes; add 1 litre boiling water and bring to a simmer
Cover and simmer until potatoes are tender (about 15 minutes), then remove the bay leaves
Purée the soup until very smooth and taste; add a pinch more sugar if needed
Cool and chill for up to 2 days or freeze for up to 3 months
Reheat the soup and stir in the milk, avoiding boiling
Serve in small bowls