Dual Colour Yogurt Sourdough Chinese Steamed Buns (Mantou), 双色优格馒头

I love to use sourdough starter to replace commercial yeast.  Thus I used it to make chinese steamed buns, mantou (馒头).  To make the mantou more challenging, I replaced milk/water with yogurt.  I'm using the stand-mixer to knead the dough.

These steamed buns can be single or double proofed.  The surface of double-proofed steamed buns tends to develop more bubbles and thus aesthetically less appealing.  So I opted to proof the dough only once.
  

Ingredients  

72g       Active sourdough starter
90g       Plain yogurt
10g       Sugar  (add more if prefer to be sweeter)
180g     Plain flour
2g         Oil of your choice
5g         Curry powder

Instructions

1.    In the stand-mixer bowl, combine all the ingredients, except the oil and curry powder.
2.    Using a pair of wooden chopsticks, stir to mix all the ingredients until a shaggy mass is formed.

3.    Add in the oil and manually knead the dough briefly.
4.    Using the stand-mixer, starting at the lowest speed, knead the dough very briefly (5-10sec).
5.    Proceed to knead the dough on the next speed for 8minutes or until the dough is soft and smooth.

6.    Weigh the dough and divide into 2, making sure one dough is roughly 10g heavier than the other.
7.    Add the curry powder to the lighter dough.

8.    Manually knead the dough briefly (30sec) and finish kneading in the stand-mixer at speed 2 until the curry powder is well incorporated into the dough (about 3-4min).

9.   Cover and rest both the yellow dough and white dough for 10min.
10.  After 10min, lightly sprinkle the rolling mat with some plain flour.  Flatten the white dough a little.
11.  Using the rolling pin, roll out the dough to form a rectangle.

 12.  Fold 1/3 of the dough onto itself.

 13.  Overlap the bottom 1/3 of the dough onto itself, forming a rectangle.

14.   Turn the dough 90°.  Repeat steps 11-13, 3 to 5 times.

15.   Flatten the dough to form a large rectangle.

 16.   Take the yellow dough and repeat steps 11-15.  Roll out the yellow dough about the same size as the white dough.

 17.  Place the yellow dough over the white dough.  Rough the dough together like making swiss roll.

 18.  Form a log dough.

 19.  Cut the uneven ends of the log dough and place on parchment paper.  Divide and cut the remaining log equally.  Put all the cut dough onto parchment papers and put them onto the steamer tray.

 20.  Fill up the steaming pot with 1/3 water.  Heat up this water to about 50°C-60°C.  

21.  Place the steamer tray, covered, on the steaming pot. 

22.  Proof for about 90min-120min or until the dough feels light when lifted.

23.  Remove the steaming trays and bring the water in the steaming pot to a boil. 
24.  Put the steaming tray back on the steaming pot.  Steam on medium low flame for 10min.
25.  Turn off the flame and rest for 3min.
26.  Remove the cover slowly.
27.  Voila!  The dual colour yogurt chinese mantou is ready for devouring.