Place the dried mushrooms in a separate bowl and cover with hot water to soak for 20 minutes or until soft. When the mushrooms are soft, squeeze them out and slice. Save the soaking water (use any extra for a future gravy base or stock).
Place the glass noodles in a bowl and cover with warm water to soak for 20 minutes. Strain water away and return noodles to bowl. Add the water or mushroom soaking water, along with the fermented tofu, vegan oyster sauce, rice wine, thin soy sauce, seasoning sauce, black soy sauce, and sugar. Toss through the noodles and set aside.
Using a pestle and mortar, pound the coriander stem, garlic, ginger, white pepper, and sichuan peppercorn (if using) together into a rough paste.
Heat the oil in a clay pot or saucepan over medium heat and saute the paste until fragrant and a shade or two darker. Turn the heat down to medium low and pour in the seasoning water. Stir to blend paste and liquid. Add tofu puffs and mushrooms, followed by the noodles. Give everything a little push with a spoon so the noodles are mostly covered in liquid. Pop the lid of the clay pot or saucepan back on.
After a couple of minutes, shuffle the noodles to evenly distribute the sauce. Place the lid back on and cook for 5-10 minutes until the noodles are done. Top with fresh herbs and chilli slices to serve.