Place dried mushrooms in a bowl with hot water and let soak for at least 2 hours until softened. (See note below)
Run cold water through the rice in a strainer. Stir the rice with your hand to wash and rinse it well until the water is mostly running clear.
Soak the rice in a bowl of water for at least 2 hours.
When ready to cook:
Combine the 3 tablespoons oyster sauce, 1 tablespoon soy sauce (or tamari), 1 teaspoon grated ginger, minced garlic clove, ½ teaspoon tapioca starch, ½ teaspoon sesame oil, and ¼ teaspoon white pepper in a bowl and mix well to make the sauce. Set aside.
Drain the rice through a colander, discarding the water.
Remove mushrooms from soaking liquid and gently squeeze out some of the water. Cut of and discard tough stems. Cut mushroom caps into slices or chunks.
Slice Chinese sausages into disks.
Heat a skillet over medium heat. Add Chinese sausage and ground pork and cook until pork is mostly cooked through.
Add mushrooms and sauce to the pan and stir. Heat through.
Add shrimp and cook until just starting to turn pink and remove from heat.
Transfer Chinese sausage mixture to the rice cooker pot and level out.
Add drained rice on top and level out.
Add 1 ¼ cups water to the rice cooker.
Cook until rice cooker button pops, or for about 25 minutes. Let sit for another 5-10 minutes. Rice should be completely cooked and slightly translucent.
Fluff rice with chopsticks, stirring well to mix the rice and filling ingredients.
Garnish with chopped green onions, if desired.
The longer you soak the dried shiitake mushrooms, the better so you can slice into them very easily and do not see any dry area inside. Soaking overnight is the easiest thing to do.
I find larger shiitake mushrooms tend to hydrate faster than small ones, but they do cost more.
You can use fresh shiitake mushrooms, but they will not have the same deep umami flavor as the dried mushrooms.
When buying the rice, the bag will either say "Thai glutinous rice" or "Thai sweet rice", or the word "Thai" might be excluded.
Use a regular 1 cup measuring cup to measure the rice; do not use the plastic measuring cup that comes with your rice cooker.
Some Chinese sausages have a dry casing that should be removed before slicing the sausage, depending on the brand and how they made it.
The dry shiitake mushrooms can be omitted, if desired.
You can use chicken thighs cut into small pieces, or cha siu in place of the Chinese sausage and/or shrimp.
I use frozen shrimp and thaw them in cold water for about 30 minutes before cooking.
To reheat any leftovers, place in a dish and steam, or microwave with a bit of water in the dish. Microwaving may dry the rice out a little, but works in a pinch.