Put dried shiitake mushrooms in a large bowl. Pour in 6 cups (1400ml) of water. Leave to soak overnight (or at least 4 hours).
Put the chicken legs (or thighs) into a pot. Add the rehydrated mushrooms, along with the soaking water (leave out any residue at the bottom of the bowl). Bring to a full boil. Skim off any foam floating on the surface.
Add Shaoxing rice wine, ginger, and the white part of the scallions. Turn the heat to the lowest. Cover the pot with a tight lid. Leave to gently simmer for 30 minutes or so until the meat becomes very tender. You may speed up this process using an Instant Pot or pressure cooker (see note 3).
Transfer the chicken legs to a plate to cool. Discard the ginger and scallions. Add light soy sauce, salt, white pepper, and sesame oil to the broth. Taste to adjust if necessary.
Once the chicken is cool to touch, remove the skin and tear the meat into bite-sized shreds.
In a separate pot, bring plenty of water to a full boil. Cook the noodles over medium-high heat until fully cooked. At the very end of this process, add bok choy for a quick blanch (20 seconds).
Drain the noodles and bok choy. Place them into 4 serving bowls. Add the broth and mushrooms. Top with the shredded chicken and the green part of the scallions (finely chopped). Optionally, drizzle some chili oil over.
Notes
1. Dried shiitake mushrooms provide an extra umami taste. If unavailable, you may use fresh shiitake or other mushrooms to substitute. In this case, cook the chicken in water and add the mushrooms at the last 5 minutes.2. Both dried and fresh noodles (made of wheat or rice flour) work well for this recipe. For one portion, use around 3.5oz (100g) of dried ones or about 6.5oz (180g) of fresh ones.3. If using an Instant Pot or a stovetop pressure cooker, cook the chicken for 10 minutes. Allow natural release of the pressure.