Heat the butter in a heavy pan. Sweat the onion for a few minutes until soft. Add the garlic and bacon. Fry for 2 minutes without browning the bacon.
Add the tomatoes and fry for a further 2 minutes. Add the other ingredients except the cream and chives. Cook, covered, for 25 minutes.
Blend or process the soup into a purée, and adjust the seasoning if necessary. Add a dollop of cream and the chives to each bowl to serve.