Roast the chicken backs and necks in a preheated oven at 400°F (200°C) for about 20 minutes to develop flavor. Add sliced ginger and chopped green onions, cover with water in a pot, bring to a boil, then simmer for 50 minutes. Strain the liquid and refrigerate overnight to set into jelly.

Combine all-purpose flour and salt in a bowl. Gradually pour in hot water, mixing until a shaggy dough forms. Add cold water little by little, ensuring a smooth consistency. Knead for about 10 minutes until silky, then cover and let it rest for 45 minutes.

Soak grated ginger in hot water for about 10 minutes. In a mixing bowl, combine jelly broth, ground pork, soy sauce, Shaoxing wine, salt, sugar, white pepper, and minced green onions. Mix thoroughly and refrigerate.

Roll the rested dough into a log and cut into pieces. Roll each piece into a 3-inch circle, place 1 tablespoon of filling in the center, pinch edges to create pleats, and seal.

Prepare a bamboo steamer lined with parchment paper, arrange dumplings inside, and steam over boiling water for 8 to 10 minutes until wrappers are translucent.