Soak mushrooms in warm water till soft. Discard the stems and cut into halves. Cut salted fish into smaller pieces. Mix the chicken pieces, mushroom halves, and sliced ginger together with the marinade. Season for at least 30 minutes (the longer, the better).
Heat up oil in a clay pot over low fire. Fry shallots until golden brown, and drain on a paper towel. Scoop out 2 tbsp of the shallot oil and set aside. Then fry the salted fish in the remaining oil until fragrant and golden brown. Scoop out and set aside.
Pour the rice grains into the clay pot and stir to mix well with the flavoured oil. Level the rice grains, and pour in the water. Cover with lid and bring to a gentle boil over low-medium heat. Let cook for 10 mins or until rice is firm (read Recipe Notes below).
Place the chicken pieces with all the marinade in a single layer on top of the rice. Then spread the sausage slices and sprinkle the crispy salted fish all over on top. Place the lid back on (read Recipe Notes below). Continue to cook for another 15 mins. Do not stir the rice.
Meanwhile, in a small bowl, combine the dark soy sauce and 2 tbsp shallot oil (from step 2 above) and stir to mix well. In a small saucepan or pot, bring some water to a boil, and par-boil the chye sim until just softened (about 10 to 15 seconds, do not overcook).
Remove the clay pot lid, drizzle half of the dark soy sauce-shallot oil mixture all over the chicken and rice, and this time, place the par-boiled chye sim on the side of the chicken pieces. Again, do not stir the rice. Place the lid back on, and continue to cook over low-medium heat for another 10 to 15 mins, or until all chicken pieces are just cooked. Remove from heat.
Drizzle the remaining dark soy sauce-shallot oil mixture liberally all over the chicken and rice. Garnish with chopped spring onions, coriander and fried shallots. Serve immediately, with extra dark soy sauce and chilli sauce on the side.