Drain and rinse the butter beans, cover with fresh cold water in a saucepan and bring to the boil. Cook rapidly for 10 minutes, then drain.
Melt the butter in a large saucepan and add the carrots, onions, leeks and celery. Cover and cook over low heat, stirring often, for 10 minutes. Add the stock, butter beans, lentils and bouquet garni and bring to the boil. Reduce the heat, cover and simmer for about 2 hours, or until the beans are very tender.
Cut a small cross in the base of each tomato and cover the tomatoes with boiling water in a heatproof bowl. Stand for 30 seconds and remove with a slotted spoon to a bowl of cold water. When the tomatoes are cool enough to handle, peel them with a small, sharp knife and discard the skin. Remove and discard the seeds and finely dice the tomato flesh.
Add the peas and tomatoes to the soup and cook for a further 10 minutes. Remove and discard the bouquet garni. Season to taste with the salt and pepper.
Ladle the soup into heated bowls, sprinkle with cheese and serve with crusty bread.