
In a large mixing bowl, whisk together the gluten-free flour, tapioca starch, glutinous rice flour, and xanthan gum until evenly combined.
Gradually sprinkle in the water while mixing with a rubber spatula. When the dough starts to come together, knead it by hand until smooth and cohesive.
Divide the dough into 4 equal pieces. Keep the dough you are not using covered tightly with plastic wrap so it does not dry out.
Roll 1 piece of dough into a log about 6 inches long, then cut it into 6 equal pieces. If you want even wrappers, aim for about 20 g per piece.
Lightly dust a wooden board and rolling pin with tapioca starch or cornstarch if needed. Roll each piece into a circle about 4 inches wide and 1/8 inch thick.
Brush the edge of each wrapper lightly with water. Place about 1 heaping tablespoon of filling in the center, then fold and pleat to seal. Set each finished dumpling on a parchment-lined tray and keep the shaped dumplings covered while you work.
For the best texture, roll each wrapper just before filling it. Once a tray is full, either cook the dumplings right away or freeze them in a single layer.
To boil, bring a pot of water to a rolling boil and stir to create a gentle whirlpool. Add the dumplings and cook until they float and the wrappers are tender, about 7 minutes for fresh dumplings or 8 minutes for frozen.
To pan-fry, heat a nonstick skillet over medium-high heat with 2 tbsp oil. Arrange the dumplings in the pan without touching, cook until the bottoms are lightly golden, then add about 1/2 cup water. Cover, reduce to medium-low, and cook for 7 to 8 minutes, or until the water evaporates. Uncover and cook briefly over medium-high heat again to re-crisp the bottoms.
To steam, line a bamboo steamer with perforated parchment paper and arrange the dumplings inside. Set the steamer over boiling water and steam for about 7 minutes for fresh dumplings or 8 minutes for frozen, then serve hot.