1Clean the ribs by covering them with water and boiling for 3 to 5 minutes. Drain and rinse the ribs, then rinse out the pot.
2Add the oil, shallots and garlic to the pot and cook until fragrant. Add half the tomatoes and cook for 4 to 5 minutes until softened and juicy.
3Add the ribs, 10 cups of water, fish sauce, bouillon, vinegar, sugar and black pepper. Bring to a boil, then partially cover and gently simmer for 45 to 60 minutes, skimming as needed.
4Add the remaining tomatoes and simmer for 5 to 10 minutes until tender.
5Taste and adjust with more fish sauce if needed.
6Cook the bún according to package directions, divide into bowls, add the ribs and tomatoes, ladle over the broth and finish with green onion, herbs, lime and chilies.