Directions

• Sprinkle oxtails with 1 1/2 teaspoons salt and pepper. Heat 2 tablespoons canola oil in a large Dutch oven over medium-high. Working in 2 batches, add oxtails; cook until browned, about 10 minutes per batch. Transfer to a large plate. Discard drippings; rinse Dutch oven, and wipe clean.
• Heat remaining 2 tablespoons canola oil in Dutch oven. Add onion; cook, stirring often, until slightly softened, about 4 minutes. Add garlic and anchovies; cook, stirring constantly, until fragrant, about 1 minute. Return oxtails to Dutch oven, and add 9 cups water, 1 tablespoon sugar, and remaining 1 teaspoon salt. Bring to a simmer over high. Reduce heat to very low; cover and simmer until oxtails are tender, about 2 hours.
• Pour oxtail mixture through a fine wire-mesh strainer into a large heatproof bowl. Set bowl aside; reserve Dutch oven. Transfer oxtails to a second large bowl; discard remaining solids. Let oxtails cool 15 minutes. Shred and set meat aside; discard bones.
• While oxtails cool, skim fat from surface of strained cooking liquid. Pour liquid into Dutch oven, and bring to a boil over high. Add peanut butter, fish sauce, annatto oil, and remaining 2 tablespoons sugar. Transfer mixture to a blender; process mixture until it reaches a creamy consistency, about 20 seconds. (Alternatively, blend mixture in pot using an immersion blender.)
• Return blended broth to Dutch oven over medium-high. Add noodles, and cook, stirring occasionally, until noodles are just tender, 5 to 7 minutes. Remove from heat. Stir in bok choy, daikon, and reserved oxtail meat. Cover and let vegetables cook in hot broth until crisp-tender, about 5 minutes. Serve hot.