The next day, by hand or by electric mixer, combine all of the bun ingredients with 1 teaspoon of salt, then knead for 10 minutes. Place in a bowl, cover with plastic wrap and proof for 1 hour. Knock the dough back and divide into 20 equal pieces. Roll into smooth balls, place on a flour-dusted tray, cover with a damp kitchen towel and proof for another hour. One by one, with a rolling pin, roll the balls into 4 x 5 inch ovals. Lay an oiled chopstick across the middle like a hinge, fold the dough in half over the top and pull the chopstick out. Place each bun on a little rectangle of parchment paper in a bamboo steamer, in single layers, read to steam later.