In a food processor, puree the beans in batches with the basil and the broth until smooth. In a large saucepan, heat olive oil and add the leeks and garlic; sauté, stirring often until the leeks are soft and begin to turn a golden colour. Add the bean puree, whole milk and the half and half cream. Stir well until soup is well mixed. Add the lemon juice and season with sea salt and freshly ground black pepper to taste. Place the soup over low heat and heat thoroughly. Serve hot. Makes 4 to 6 servings.