In a large mixing bowl, mix yeast with flour. Stir in warm water. Combine all the ingredients and then knead into smooth dough. Cover and rest for 15 minutes.
Cover the dough and rest for 15 minutes until slightly softened. Cut the dough into halves. Wrap and transfer the other half in fridge. And re-knead one half for 2-3 minutes. Shape the dough into a long log and then cut into 12 equal portions. Roll each of the portion to large wrappers and then assemble well. After assembling, let the buns rest for another 15 minutes.
Add hot water to ginger, scallion and Sichuan peppercorn to make the ginger scallion water.
Add the pork, salt, ground pepper, sugar, soy sauce, cooking wine and oyster sauce in. Blend for 2-3 minutes with stopping. Then add ginger and scallion water by 2 batches. Blend until the water is completely absorbed. Transfer the filling out, mix with 1 tablespoon of sesame oil. Then chop the pork jelly and mix well.
Assemble the buns according to this direction one by one. Brush some oil on your pan firstly and transfer the assembled buns to the pan. Do leave some space between each one. Cover with lid or a wet cloth and rest the buns for around 15 minutes.
Fry for around 2 minutes until the bottom is crispy; pour starch water and cover the lid to cook for around 5-6 minutes until the water are completely evaporated so that the buns will be cooked thoroughly. Sprinkle roasted black sesame seeds and green onions.