Slice and Dry: Slice fish into ½-cm slices on a bias. Pat thoroughly dry with paper towels — this is the key to the coating staying on.
Coat: Mix fish gently in one direction with salt, white pepper, and Shaoxing wine until slightly tacky. Mix in egg white and cornstarch to coat, then toss with neutral oil. Rest 10 minutes.
Aromatics: Sauté ginger, garlic, and the white/light green scallion parts in a little oil until fragrant. Transfer to the clay pot and layer tofu slices over the bottom.
Broth: Add boiling water (or stock) and whisk in bouillon and/or miso (if not using stock) until dissolved. Add broccoli stems (if using). Boil, then reduce to a gentle simmer. Season the broth to taste with salt and white pepper. (Optional: simmer kombu or shrimp shells briefly for a fishier broth, then remove.) Simmer for two minutes.
Fish: Reduce to the lowest heat. Lay fish slices one at a time over the tofu using tongs or chopsticks. Do not stir.
Finish: When the fish edges turn white, cover and turn off the heat. Rest 1-2 minutes on residual heat. Finish with sesame oil and sliced scallion greens. Serve hot.