1, To make the filling, in a skillet, heat the oil over medium heat. Add the onion and sauté for 1 to 2 minutes, or until soft and fragrant. Add the pork, pressing and poking it to break it up into small pieces, and sauté for about 1 minute, or until half cooked. Add the wood ear mushroom, shiitake mushrooms, and shrimp, stir to combine, and then sprinkle in the fish sauce, salt, and pepper. Continue to sauté for 2 to 3 minutes, or until the shrimp turn pink. Transfer to a bowl and set aside for about 45 minutes, or until completely cooled. (The filling may be prepared up to 1 day in advance and stored in an airtight container in the refrigerator. Bring to room temperature before using.)
2, To make the batter, in a bowl, stir together the cornstarch, tapioca starch, rice flour, and salt. Make a well in the center, pour in the oil and water, and whisk together all the ingredients to make a thin, smooth batter. There should be about 3 ¾ cups. Let the batter rest for 30 minutes.
3, Organize your cooking station before you begin making the rolls. Set the batter and oil on one side of the stove and the filling on the other side. Nearby, spread out a dish towel on a countertop and invert a baking sheet on top of it, close to the edge of the counter. You need to use a sturdy baking sheet because you will be banging the skillet against it. Lightly brush the baking sheet with oil. Have ready a platter for holding the finished rolls.
4, For each crepe, brush an 8-inch nonstick skillet with ¼ teaspoon of the oil and place over medium-low heat. The skillet is ready when a bit of batter flicked onto it gently sizzles.
Give the batter a good stir and ladle 2 ½ tablespoons into the skillet, quickly swirling the pan to coat the bottom evenly. Cover and allow the crepe to steam for about 45 seconds and then uncover. The crepe should be translucent, bubbling (or even ballooning), and gently sizzling. (Replace the lid if it is not.) Cook for 30 to 60 seconds more to dry the crepe slightly and help it release. A longer cooking time yields a firmer crepe that releases nice and flat. For a slightly softer crepe, use a shorter cooking time, but keep in mind that it may fall out slightly wrinkled and need to be straightened out before filling and rolling.
When the edges have pulled away from the skillet— the crepe will still look wet— pick up the skillet and quickly invert it onto the baking sheet, banging it to release the crepe. Return the empty skillet to the burner to reheat, adjusting the heat as needed. At the beginning, expect to tinker with the heat, the level of which depends on the skillet and the stove. Lower the heat slightly if huge craters form when the batter hits the skillet. Aim for crepes that look like relatively smooth white sheets.
5, Once you have banged the crepe out of the pan, immediately turn your attention to filling and rolling it while it is still a bit slippery and easier to manipulate. The slight stickiness helps the crepe to seal. If it didn’t fall out flat, do your best to straighten out any wrinkles with your fingers. (It is not that hot.) Fold up the bottom inch of the crepe. At the top edge of that flap, center 1 tablespoon filling, spreading it out horizontally and leaving 1 inch of space on both sides. Fold in the side flaps to cover the filling partially. Lift the bottom edge over the filling, and then roll it up to seal. The finished roll is shaped like a stubby 3 ½-inch-long cigar, with the filling visible on top. Place the roll on a plate or platter. Before making another roll, brush more oil on the skillet and on the baking sheet.
Once you have made a few rolls, you will establish a rhythm for steaming, filling, and rolling. Remember that imperfections are hidden once the crepe is rolled; if one side got bunched up or is particularly wrinkly, fill and roll from that direction. Hide ragged edges by folding them inward.
6, To serve, divide the rolls among 4 plates. (You may reheat them in a microwave oven until just warm, not hot.) Garnish with a sprinkling of the pork, followed by the cilantro, and then the shallot. Instruct diners to drizzle the dipping sauce directly onto the rolls. Use chopsticks or a fork and knife for eating.