1. In a large pot, combine all stock ingredients. Simmer, uncovered, over low heat for 1 hour. Strain, pressing on vegetables to extract juices. Discard vegetables and set liquid aside.

2. Blanch fava beans for 30 seconds and pop them out of their skins; set aside. If favas are young and tender, they'll require very little further cooking.

3. Pour stock into a large saucepan over medium heat. Add limas and bring to a simmer. Cook until beans are tender, about 15 minutes. Season with salt and pepper. Bring liquid to a boil and add pasta; cook until al dente. In the last minute of cooking, add tomatoes and favas.

4. Roll mint and basil leaves tightly and slice thin, to achieve a fine chiffonade; ladle soup into bowls and garnish with a generous pinch.