Instructions

1. 1
   Combine the flour, sugar, salt, baking powder, and yeast in a bowl.
2. 2
   Add the water and milk. Mix until you get a sticky dough.
3. 3
   Turn the dough out onto a work surface, and knead well for 10 minutes. The dough should no longer be very sticky once you have finished.
4. 4
   Transfer the dough back to a bowl, and cover with plastic wrap or a damp towel. Let rest in a warm place for 1 hour or until doubled in size.
5. 5
   Gently deflate the dough, and transfer it to your work surface.
6. 6
   Roll the dough into an even sausage shape, and cut into 15 equal pieces.
7. 7
   Roll each piece into a ball, then flatten and roll with a rolling pin into an oval. The oval should not be too much longer than it is wide.
8. 8
   Brush the ovals with oil, then fold each in half with the oil on the inside. It should look like a taco shell or a purse. Don't pinch the edges together.
9. 9
   Cover the buns with greased plastic wrap, and let rest for 20 minutes.
10. 10
    Bring a few inches of water to a boil in a steamer. Place the buns in the basket, and steam for 20 minutes.
11. 11
    Remove from the steamer.
12. 12
    Heat a skillet over medium heat, and add 2–3 tablespoons of vegetable oil.
13. 13
    Add the onions to the pan, and stir to coat with the oil.
14. 14
    Cover the pan, and turn the heat down to medium-low. Let the onions cook, stirring occasionally. As they cook, they should wilt and start to soften. Keep stirring every couple minutes to distribute the browning that accumulates at the bottom of the skillet and prevent burning.
15. 15
    Once the onions are a light golden color (it will take a while—be patient), remove the lid and continue cooking until deeply browned to your liking. Note that the more browned they get, the greater the risk of sticking and burning to the pan—pay attention near the end.
16. 16
    Remove the caramelized onions from the heat and set aside.
17. 17
    Heat a skillet over medium heat, then add 15 ml (1 tbsp) vegetable oil.
18. 18
    Add the mushrooms, and fry over medium heat for 3–4 minutes until softened.
19. 19
    Stir in the sesame oil, caramelized onions, ginger, garlic, vinegar, soy sauce, stock, maple syrup, and chile flakes. Cook for another 5–6 minutes until everything is soft and fragrant.
20. 20
    Remove the filling from the heat.