In a saucepan, heat stock until it boils, then gradually mix in gelatin in batches and stir until completely dissolved.
Pour out into a tray or container to cool down.
Place aspic in the chiller for at least 2 hours.
When the aspic is firm and set, chop it into small cubes.
In a bowl, mix minced chicken, egg, ½ tsp salt, 3 tbsp light soy sauce, minced ginger, 2 tsp sesame oil and chopped aspic until well combined. Set aside.
Dissolve ½ tsp salt in 340 ml warm water.
Mix salted water into flour to form a soft dough.
Knead dough with 1 tbsp oil. Cover dough in plastic wrap and leave in warm place to rest for 30 minutes.
Transfer to a lightly floured surface and knead for 10 minutes, adding more flour as needed to prevent sticking, until dough is soft, smooth, and slightly sticky.
Divide dough into 4 equal pieces. Working with 1 piece at a time and keeping other pieces covered with plastic wrap, roll out dough with your palms to make long ropes.
Divide dough into 20 g balls and flatten with a rolling pin, about 6 cm in diameter.
Spoon ½ to 1 tbsp filling in the middle of dumpling wrapper.
Using fingertips on one hand, gently pull and stretch wrapper outward before bringing it in to meet opposite fingers.
Carefully fold stretched area in on itself, creating a pleat. Pinch to seal pleat and repeat until dumpling is completely sealed.
Lay parchment paper on the bottom of steamer basket and place dumplings over. Steam for 15 to 20 minutes.
In a sauce dish, add 1 tbsp black vinegar with finely sliced ginger. Serve dumplings in steamer basket with dipping sauce on the side.