Mix the seasoning ingredients in a bowl until well-combined.
Prepare the filling: Heat a large non-stick pan and add a tablespoon of oil. Sauté tofu and mushrooms until golden brown.
Add the carrot, celery, preserved radish, chestnut, and keep cooking for another minute or so.
Season with the prepared sauce and stir-fry to combine. Stir in the cornstarch slurry and turn off the heat. Turn off the heat and transfer the mixture to a bowl.
Fold in the chopped Chinese chives and toasted peanuts. Taste test and season accordingly if needed. Set aside to cool down.
To make the dumpling wrapper, stir the wheat starch, tapioca starch, sweet potato powder, and salt in a bowl until well-combined.
Fill a pot with 250ml water and bring it to a rolling boil.
Using a rolling pin, stir the hot water into the dry ingredients until well-combined. Note: When you add in the hot water, some flour will immediately turn translucent.
Try to gather as much flour from the bowl as possible to make a dough. If the dough appears too dry, add some room temperature water, one tablespoon at a time.
Then, add the oil and knead until all is incorporated. Cover the bowl with a tight lid and rest for 5 minutes.
Meanwhile, cut out 10 (4x3-inch) parchment rectangles and set aside.
Lightly flour a work surface with tapioca starch. Uncover the dough and knead into a soft dough then divide it into 10 equal pieces.
Work with one dough at a time and keep the rest of the dough in a tightly covered bowl to prevent them from drying out.
Roll each dough into a 4-inch diameter circular wrapper with a thick middle. Please see the video for the visual instruction.
Place a heaping spoon of filling in the middle and pleat to seal then transfer to a parchment paper.
Fill the steamer pot with water and bring it to a rolling boil.
Transfer the wrapped dumplings to the inner steamer rack and place them in the steamer.
Steam over high heat for 10 minutes. Uncover the lid and brush a thin layer of shallot oil to prevent the dumplings from drying out.
Serve warm with a side of hoisin and chili sauce.