01 - Whisk together rice flour, tapioca starch, cornstarch, salt, water, and vegetable oil in a bowl until completely smooth and free of lumps. Let the batter rest for at least 20 minutes to achieve proper consistency.
02 - Heat 1 tablespoon oil in a skillet over medium heat. Sauté onions and garlic until fragrant, about 1 minute. Add ground pork and cook until browned. Stir in chopped wood ear mushrooms, fish sauce, and pepper. Continue cooking for 2-3 minutes until fully cooked and fragrant. Remove from heat and set aside.
03 - Combine fish sauce, lime juice, sugar, and warm water in a small bowl, stirring until sugar completely dissolves. Add minced garlic and sliced chili. Taste and adjust seasoning if needed, balancing sweet, salty, and sour flavors.
04 - Bring water to a boil in a wide steamer or large sauté pan with a nonstick, lightly oiled cloth or silicone tray placed on top. Ladle approximately 1/4 cup batter onto the surface, swirling quickly to create an even, thin layer. Cover and steam for 1-2 minutes until the sheet is set and slightly translucent.
05 - Using a thin spatula or offset spatula, gently lift the cooked rice sheet onto a lightly oiled plate. Place a spoonful of filling along one edge of the sheet and roll up tightly to enclose the filling. Repeat with remaining batter and filling, working quickly to maintain optimal texture.
06 - Arrange completed rolls on a serving platter. Generously top with fried shallots, fresh cilantro, bean sprouts, sliced cucumber, and pork sausage if using. Serve immediately with nuoc cham dipping sauce on the side for best texture and flavor.