Start by mixing the plain flour, cornflour, and salt in a large bowl. Gradually add water and knead until you have a firm yet soft dough. It might feel a little stiff at first, but keep kneading for about 10 minutes until smooth and elastic. Cover with a damp cloth and set aside for an hour to rest.
While the dough rests, prepare the filling. Combine the ground chicken, garlic, ginger, spring onions, onion, lemongrass, coriander, chilies, ground cumin, soy sauce, salt, and pepper. Use your hands to mix everything thoroughly, ensuring the seasoning is evenly distributed.
Divide the dough into smaller pieces, roughly the size of a golf ball. Roll each piece into a thin circle, about 2mm thick and 9cm in diameter. This will create the perfect base for your filling.
Spoon a small amount (about a tablespoon) of filling onto each dough circle. Wet the edges with a little water, fold the dough in half to form a semi-circle, and pinch the edges shut. Pleat the edges for a decorative finish and a better seal.
Place the momos in a steamer, ensuring they don’t touch each other. Steam for about 6 minutes. The wrappers should turn translucent when fully cooked. Work in batches if necessary.