• In the morning, feed your sourdough starter.
• Once the starter has risen, mix all the dough ingredients in a large bowl and use a fork to combine it into a shaggy dough. Once you can't mix with the fork, switch to using your hands.
• Combine it all together into a thick and stiff dough. If it's too thick to mix, wet your hands to add a little more water to the mixture. The dough will be very thick. Knead the dough on the bench until it is soft and smooth. Form a dough ball and place it into a bowl.
• Let the dough rise in a warm spot until it has bulked out by around 50%. You can create a warm and humid spot by placing the dough in a turned-off oven next to a mug of boiled water. This can take around 4 hours in a warm space.
• After this rise, cover the bowl tightly with plastic wrap and place it in the fridge overnight. You can skip the cold proof and go right to cutting and shaping but the flavour will be milder and the dough a bit softer to work with.

The Following Day

• Pull the dough from the bowl and place it on a clean bench. Roll the dough out into a large circle, about 5mm thick, and use a circle cutter (I use a drinking glass) to cut out dough circles. (If necessary, use a little flour to dust the bench lightly.)
• Once you’ve cut all the circles you can, gather the remaining dough into a ball and leave it to sit and rest for 10 minutes before rolling it out again.
• Roll a cut-out circle to create an oval around 3-4mm thick. Fold it in half. I place a small slip of parchment paper in between the fold so it doesn't stick together. Place the shaped bun on a tray lined with parchment paper. Continue with the remaining dough circles. 
• Let the buns rise again until puffy. Once risen, cut around the risen buns on the baking paper so each bun is on a separate piece. This makes them much easier to lift in and out of the steamer.
• Fill a large saucepan or pot with 3-4 cm of water and bring it to a boil. Place the buns in the steamer 2-4 buns at a time (depending on the size of the steamer.) Add the lid to the steamer, then place it over the boiling water. Leave the buns to steam for around 10 minutes.
• Take the steamer off the saucepan, remove the lid, and lift the cooked buns. Repeat these steps with the remaining buns.
• If making these ahead, they can be reheated by being placed back in a steamer for 2-3 minutes until warmed.  Pry them open along their fold, then stuff them with your favorite fillings. They can also be frozen for future use.