Authentic Bún bò Huế (Spicy Vietnamese Beef Noodle Soup)

Bring a large pot of water to a boil. Add beef shank and pork hock; boil for 5 minutes to remove impurities. Drain and rinse under cold water. Clean the pot.

Return cleaned meats to the pot with 2.5 liters water, bruised lemongrass, shallots, and garlic. Bring to a boil, then reduce heat to a simmer. Skim any foam that rises. Simmer for 1.5 hours until meat is tender but not falling apart.

Remove beef shank and pork hock; let cool slightly. Slice beef against the grain into thin pieces and cut pork into manageable chunks. Set aside. Strain broth through a fine sieve; discard solids.

In a small pan, heat vegetable oil over low heat. Add annatto seeds; cook until oil turns rich orange-red (about 5 minutes). Strain oil through a fine-mesh strainer, discarding seeds.

Return strained broth to pot. Add fish sauce, salt, sugar and chili flakes. Stir in annatto oil. Taste and adjust seasoning—it should be savory with a warm spiciness. Keep warm.

Cook rice vermicelli according to package directions until just tender. Drain and rinse under cold water to prevent sticking.

Divide noodles among bowls. Top with sliced beef shank, pork hock, and pork blood (if using). Ladle hot broth over the top.

Serve immediately with bean sprouts, banana blossom, mint, cilantro, and lime wedges on the side. Let diners add what they like.