If using live crabs, humanely dispatch them by plunging into boiling water for 1-2 minutes, then immediately transfer to an ice bath. Once cooled, clean the crabs: remove the top shell, gills (dead man's fingers), and mouthparts. Rinse thoroughly under cold running water. Using a cleaver or heavy knife, cut each crab body into 4-6 pieces, keeping the claws and legs intact. Crack the larger claws slightly to allow flavor penetration.

Heat vegetable oil in a large stockpot or Dutch oven over medium heat. Add the thinly sliced ginger and the white and light green parts of the scallions. Sauté for 3-4 minutes until fragrant, being careful not to brown them.

Pour in the chicken or seafood broth and Shaoxing rice wine. Bring the mixture to a simmer. Add the soy sauce, toasted sesame oil, white pepper, and salt. Stir well and let it simmer gently for 10 minutes to allow the flavors to meld.

Carefully add the prepared crab pieces to the simmering broth. Ensure the crab pieces are mostly submerged. Cover the pot and cook for 8-10 minutes, or until the crab shells turn bright orange-red and the meat is opaque and cooked through. Avoid overcooking, as the crab meat can become tough.

Taste the soup and adjust seasonings (salt, white pepper) if needed. Ladle the hot crab soup into individual serving bowls, ensuring each bowl gets a good mix of crab pieces and broth.

Garnish generously with the reserved dark green parts of the scallions and fresh cilantro. A drizzle of chili oil can be added for a touch of heat, if desired. Serve immediately.