Put the pork on a large cutting board and very finely mince it with a sharp, heavy knife or cleaver until the fat is broken down (or use 2 large heavy cleavers to get the job done quicker!). Spread out the pork into a thin layer on the board. Grate the ginger, shallot and bouillon over the meat using a fine grater, and then sprinkle on the cornstarch, five-spice, Shaoshing, salt, pepper and egg yolk. Mix well until combined using a knife or spatula.
Put some cornstarch in a shallow bowl. Roll the pork mixture into ping pong ball-size meatballs, and then roll in the cornstarch to lightly coat. Shake off the excess and transfer the meatballs to a plate.
Using wet hands, put some of the soaked rice in your palm and roll the meatball in it with your hands, pressing gently, until evenly coated in rice. Continue rolling until the meatballs are all coated with the rice.
Fill a wok one-third full with water and bring to a boil over medium-high heat. Put a shallow flat bowl or plate with a lip into a bamboo steamer basket (make sure the plate is at least 1/2 inch smaller than the diameter of the basket) and evenly space the rice balls on the plate, being sure they do not touch each other. Cover the basket with the lid and lower it into the wok. Steam the meatballs, adding water to the wok as necessary to prevent the basket from scorching, until set and firm, 20 to 25 minutes.
Carefully remove the rice balls from the steamer and transfer to a platter. Serve the meatballs with toothpicks on the side for skewering and dipping into vinegar, chili oil, or soy sauce.
You can also put the finely chopped pork into a standing mixer fitted with a paddle attachment and whip it to break down the fat and make a smooth, tender meatball. Add the flavoring ingredients and whip slowly until combined before rolling and steaming the pearl balls. They can also be steamed on a vegetable steamer basket fitted inside a large pot with a lid.