Directions:

• Preheat oven to 350�F. Cut 1/2 inch off tops of garlic heads to expose cloves. Place garlic and onion halves, cut side down, on an aluminum foil�lined baking sheet. Roast in preheated oven until very tender and cut sides of garlic and onion halves are caramelized, 45 minutes to 1 hour.
• Meanwhile, bring 8 quarts water to a boil in a large stockpot over high. Stir in 1/4 cup salt, and return to a boil. Add oxtail, pork bones, and short ribs. Cover and return to a boil over high. Uncover and boil, undisturbed, until foam rises to surface, 3 to 5 minutes. Drain oxtail mixture in a colander, and rinse under cold running water to remove excess foam; set aside. Wash pot.
• Add remaining 8 quarts water to pot; bring to a boil over high. Stir in brisket, lemongrass, rock sugar, roasted garlic and onion, oxtail, pork bones, short ribs, and remaining 3 tablespoons salt. Bring to a boil over high. Cover and reduce heat to low. Simmer, stirring occasionally and skimming off any foam that rises to surface, until a thermometer inserted in thickest portion of brisket registers 200�F, about 45 minutes.
• Fill a large bowl with ice water. Transfer brisket to ice water (to stop cooking and give meat a firmer texture). Let stand 5 minutes. Remove brisket from ice water, and pat dry; wrap tightly in plastic wrap. Chill until ready to serve, up to 3 days.
• Increase heat under broth to medium, and gently simmer, uncovered, skimming fat occasionally, until broth is deeply flavored and meat is tender, about 2 hours. Remove from heat.
• Working in batches, pour simmered broth through a cheesecloth-lined fine wire-mesh strainer into a large pot. Transfer short ribs and oxtail to a plate; set aside, and let cool about 15 minutes. Discard remaining solids. Bring strained broth in pot to a simmer over medium, adjusting heat as needed. Simmer, uncovered, about 30 minutes, occasionally skimming fat that rises to surface but leaving a small amount for flavor.
• Using a mortar and pestle or a spice grinder, grind crushed red pepper and annatto seeds into a coarse powder. Heat oil in a medium skillet over medium. Stir in annatto seed mixture. Add shallots, lemongrass, and shrimp paste. Cook, stirring often, until shallots begin to soften, about 2 minutes. Remove from heat.
• Stir annatto seed mixture into simmering broth in pot. Cook, stirring occasionally, 5 minutes. Stir in fish sauce and salt. Season with sugar, fish sauce, and additional salt to taste. Simmer over medium, undisturbed, until flavors meld, about 20 minutes.
• While soup simmers, prepare noodles according to package directions. Thinly slice brisket, and pull oxtail meat from bones; discard bones. Remove short rib meat from bones; slice meat, and discard bones.
• To serve, arrange 1 cup noodles in each serving bowl, and top evenly with cha lua and other meat. Ladle broth evenly over top. Sprinkle with scallions; serve with desired toppings.