Char siu bao 'smiling'

I have several pork bao recipes but for char siu bao, I've never really found the trick. I have recently found that the trick is wheat starch. This recipe is very detailed and has researched several sites, including the 'seminal' recipe by Lydia Teh. Everybody eats well. I also found another recipe by RasaMalaysia but it seems that someone is copying someone... not sure who. The instructions are very similar (sometimes even word for word) and the ingredient list and weights are exactly the same.

The advice is also similar (rephrased here):

1. The baking powder must be well dissolved in the cold water, otherwise it will leave yellow spots.
2. To get a white bao, first, use lard rather than oil. It just happened that I have some lard sitting around after a roost pork crackling dinner. Second, use HK flour or cake flour rather than normal flour. Cake flour has a lower gluten level than HK flour. Both are bleached. I don't have HK flour on hand (without running out to the Asian grocer) and I've tried cake flour and it was terrible to work with. So I'll probably stick to normal flour (which EEW doesn't recommend).
3. Use some vinegar in the steaming water, also for apparently whiter baos. I've tried this both with and without and no difference.
4. Only steam the baos when the water has come to a rolling boil, otherwise the baos won't rise properly. Do not open the lid during steam and cover the lid with a cloth so that the condensation doesn't drip on the surface of the buns.
5. Spray the buns with a water mist after proofing but before steaming to produce even fluffier baos.

I realised I used this exact char siu bao recipe from Rasa Malaysia when I adapted for Kimchi Pork Buns but this time I'm following the recipe more closely.

Smile or burst?

Ingredients 
For Bao (16x3" bao)
2.5 tsp (8g) instant yeast
280g normal flour, remove 4 tbsp of the flour and add 4 tbsp corn flour
100g wheat starch
160ml warm water (warm to the touch)
½ tsp white vinegar
2 tbsp sugar (original recipe was 90g icing sugar)
Pinch of salt
30g shortening (I used lard)
2 tsp (10g) baking powder
10ml cold water

Char siu: I had leftover from here and even the sauce.
250g char siu
1 chopped small shallot
approx 175ml of sauce (char siu sauce, including 150ml water and 1.5 tbsp corn starch)

Prepare: 3 by 3" parchments. Prepare steaming wok. Wrap the cover in a cloth.

Method
1. Sift together the flours and add the sugar. Mix well. Add the yeast and salt (do not put one on top of the other or the salt deactivates the yeast). Mix well.
2. Create a well in the middle. Pour in the water and vinegar. Bring together with a spatula or chopstick.
3. Add the shortening and knead for 10 to 15 minutes until smooth and no longer sticky.
4. Cover with cling film and proof until doubled in size (about 40 mins to 1 hour).
5. Dissolve the baking powder in the COLD water. Ensure there are no lumps and well dissolved. Sprinkle onto the surface of the buns and knead well. Rest for 10 minutes.
6. Divide dough into 16 portions. Roll out into 4" circle. Using the Asian rolling pin, leaving it slightly thinner at the edges and thicker in the centre.
7. Spoon one heaped tbsp into the centre and pleat. Place on pre-prepared parchments of 3 by 3". Cover and rest for at least 15 minutes.
8. Meanwhile your water should already be heating up. When it has come to a rolling boil, steam the buns on high heat for 10 to 12 minutes. Turn off the fire and rest for 5 minutes.
9. Remove and serve immediately. Best eaten hot. Store in fridge for up to 4 days. EEW doesn't recommend freezing but I find no problem, as long as they are frozen immediately when cool (rather than left lingering in the fridge). They can be reheated from frozen, approx 2 minutes on one side and turn.

Recipe feedback
- Misting the bao was definitely the wrong idea because it made the bao soggy.
- The mix of flour, corn starch and wheat starch made the bao very flat, no different to when cake flour was used.
- However, the use of wheat starch meant that the dough was a lot more manageable and handleable. It was very stretchy and I could make very nice pleats. Problem is that it was so thin that it tore, which is also why I couldn't seal it properly.
- The bao was already leaking before I even put it in the steamer, so it didn't really burst. I was probably too generous with the sauce.
- Was the dough fluffy like dim sum char siu however? It wasn't. It was a great fluffy bao but it wasn't the dim sum bao. For the first time, I actually think there wasn't enough dough on top! Maybe I should do what I've seen in some other receipe and put my pleats facing down instead so that if it leaks, it will leak onto the paper. The top may or may not open up and 'smile' but at least it wouldn't leak.