To make the dough, combine the water, yeast, a tablespoon of flour and sugar and set aside for 10 minutes for the yeast mixture to become frothy.
In a large bowl, sift the flour, add the yeast mixture, oil and salt and knead well for about 5 minutes, until the dough becomes elastic and does not stick to the hands - use a bit more flour if necessary.
Shape the dough into a ball.
Lightly oil the bowl and the dough, cover with clingfilm and a clean tea towel and leave to prove in a warm place for 1-2 hours, until the dough doubles its volume.
Heat up the vegetable oil in a wok.
Chop the spring onions, garlic clove and ginger, and stir fry for 1 minute.
Add the finely chopped pork, and give it a good stir
Mix in the soy sauces, sesame oil, sugar and white rice vinegar, and leave it to cook for 1-2 minutes.
Remove from the pan and allow the filling to cool.
Transfer the dough to the work surface, roll it so it can have about ½ cm thickness, then cut it in rounds of 6 cm in diameter.
Place a teaspoon of the filling in the middle of each circle, then seal well with your fingers, and shape into small balls.
Preheat the oven to 200 degrees C. (390 degrees Fahrenheit).
Arrange the balls on a baking tray, brush the buns with the beaten egg and sprinkle over the sesame seeds.
Bake for 15 minutes until golden.
Serve warm!