1. For the pork: Turn on the barbeque to high heat.
2. Lather the pork in all ingredients except for chicken stock and tonkatsu sauce. Excess marinade time is not necessary.
3. Remove pork from marinade and grill all over until blackened.
4. Place pork (skin side down), excess marinade, and chicken stock in a slow cooker on a low setting for 8 hours. The liquid will not entirely cover the pork, but that is fine.
5. Remove pork from liquid. Chill it down in the fridge. Reduce remailing liquid by ¾ and allow to cool.
6. When pork is chilled, remove skin and dice very fine. Dice pork into 1cm x 1cm cubes.
7. Mix together with reduced cooking liquor and tonkatsu, and refrigerate (ensuring mix is fully chilled before filling the buns).
8. For the dough buns: Cut 8 squares of baking paper at 15cm x 15cm. Set aside.
9. Melt butter and allow to cool to about body temperature.
10. Add dried yeast to milk.
11. Add dry ingredients to bowl of a stand mixer (dough hook attached).
12. Mix on low speed. Add milk mix over 30 seconds.
13. Add eggs one by one.
14. Pour in butter. Mix for about 4 minutes, until dough is silky smooth, soft and elastic.
15. Put dough in a clean bowl (at least twice the size of dough). Wrap well and allow to prove at room temperature for about 90 minutes, or until nearly doubled in size. At this point, refrigerate the dough for 1 hour (it will be much easier to work with).
16. Turn dough onto a clean bench. Cut into 40g portions and roll into balls. Any excess dough balls can be used to make yuzu and ricotta donuts (p.48), or stored in an airtight container and frozen for a later use.
17. With a floured rolling pin, roll the balls into a disc, about 12cm in diameter.
18. Scoop out 40g portions of the chilled sticky pork mix, and shape them into balls. Place the balls of pork mix in the center of your dough discs.
19. Using lightly floured hands, pinch and stretch the dough over the pork. Continue pinching and stretching the edges around the filling, sealing the dough tightly around the pork.
20. Turn the buns onto pre-cut baking paper, seam-side down. Place buns in a baking tray and spray tops of buns with canola oil.
21. Cover and allow to prove again at room temperature, approx. 1 hour.
22. Bring a pot of water to rapid boil.
23. Gently pick up buns by their paper sheets underneath and place in steamer basket, allowing some excess room to swell as they steam. Place basket over boiling water, and with lid on, steam for 9–10 minutes. Bun dough should look inflated and lightly bounce back when pressed.
24. Allow to cool slightly and serve with hot sauce and soy.