Melt butter in large saucepan, add onions and heat gently for about 5 minutes or until soft and tender. Add carrots, stir to coat with butter and cook a further 2-3 minutes. Stir in flour and cook for 1-2 minutes then gradually add stock and bring to a boil. Season to taste with salt and pepper and add the coriander, bay leaf, and lemon juice. Cover the pan and simmer gently for 30 minutes or until the carrots are very tender. Discard the bay leaf and puree soup in food processor. Pour soup into a clean pan with the milk and return to a boil. Once boiled turn off heat and taste. Adjust seasoning as required. Stir in the cream and reheat gently. Serve at once in warmed soup bowls. Garnish with parsley. If you wish to freeze the soup, do so before you add the milk.