Direction

1. Peel and devein shrimp; place shells and tails in a medium saucepan. Cut each shrimp in half lengthwise. Place shrimp on a plate, and refrigerate until ready to use.
2. Add smashed scallions, ginger, and 4 cups broth to shrimp shells. Bring to a rolling boil over medium-high. (Remove chicken from refrigerator, and let stand at room temperature while broth comes to a boil.) Boil, stirring occasionally, until flavors meld, about 5 minutes. Add chicken breast. Cover saucepan tightly with lid, and remove from heat; let stand until chicken feels firm yet still yields a bit to the touch and a thermometer inserted in thickest portion of meat registers 155°F, about 20 minutes. Using a slotted spoon, transfer chicken to a plate, and loosely cover with aluminum foil; set aside. Pour broth through a fine wire-mesh strainer into a large (5-quart) pot; discard solids. Cover and set aside.
3. Rinse medium saucepan, and fill halfway with water. Bring water to a boil over high; add rice, stirring to separate grains. Boil over high, undisturbed, until tender but still firm, about 8 minutes. Drain rice, and set aside. Rinse and dry saucepan.
4. While rice cooks, soak mushrooms in hot water until softened, about 15 minutes. Drain and cut into thin (1/8-inch-wide) strips.
5. Add remaining 8 cups chicken broth to warm broth in pot. Bring to boil over high; stir in mushrooms and reserved rice. Reduce heat to medium-high; gently boil, undisturbed, until rice grains are plump and start to split at ends, about 10 minutes. Remove from heat.
6. While rice cooks, heat oil in a medium saucepan over medium. Add shallot, and cook, stirring occasionally, until fragrant and soft, 3 to 5 minutes. Add reserved shrimp; cook, stirring often, until shrimp are just cooked and turn opaque, about 2 minutes. (Shrimp will curl into a corkscrew shape.) Remove from heat, and add crabmeat to shrimp mixture. Hand-shred reserved chicken into saucepan. Set aside.
7. Place tapioca pearls in a fine wire-mesh strainer, and rinse briefly under cold water. Stir tapioca pearls into rice mixture in pot; return to heat over medium-high, and cook, undisturbed, until soup is slightly thickened and opaque tapioca pearls have expanded and are mostly clear, about 10 minutes.
8. Stir chicken mixture into soup in pot; cook over medium-high, undisturbed, until heated through, about 1 minute. Season with salt to taste. Add up to 1 cup water as needed for soup to reach desired consistency. Remove from heat, and ladle soup evenly into 8 individual bowls or a large bowl or tureen; garnish with sliced scallions and cilantro. Serve immediately.