To make the dumplings, sift the flour into a large bowl. Make a well in the centre and pour in the water. Using your fingers or a spatula, draw the flour into the liquid until it has been incorporated and the dough comes away from the sides of the bowl. Turn the dough out on to a lightly floured surface and knead for 5 minutes, or until it is smooth and elastic. Return to the bowl, cover and set aside for 30 minutes.

Heat the oil in a large frying-pan. Add the spring onions (scallions), ginger, mushrooms and crabmeat and stir-fry for 3 minutes. Stir in the remaining ingredients and fry for a further 1 minute, stirring constantly. Remove from the heat and set aside.

Turn the dough out on to the floured surface and roll out into a sausage about 2 1/2 cm (1 in) in diameter. Cut the dough into slices about 2 1/2 cm (1 in) wide. Flatten the slices evenly with your fingers until they measure about 7 1/2 cm (3 in) in diameter.

Place a teaspoon of filling on one side of each dough circle. Fold over the circles to make a semi-circle and pinch to seal.

Half-fill a large saucepan or the bottom half of a steamer with water. Bring to the boil over high heat. Arrange the dumplings in a colander or the top half of the steamer and place over the boiling water. Reduce the heat to moderate and steam the dumplings for about 10 minutes.

Transfer to a warmed serving dish and serve at once.