Add in the ground beef and break it up with the back of a wooden spoon. Sauté until the beef releases some oil, about 2-3 minutes (if you use regular, you may need to blot excess grease with a paper towel).
Lower the heat to medium, add the onion and garlic to the beef and continue to sauté until onions soften and aromatic, another 4-5 minutes.
Season the meat with salt and sugar.
Add in the curry powder and stir to coat the beef, cooking for 1-2 minutes. Reduce the heat to medium low.
Add in the soy sauce. Stir to incorporate the mixture.
Pour in ¼ C beef stock and scrape off any brown bits stuck to the pot.
Give it a taste and adjust to your preference.
Remove the beef mixture from heat and transfer to a bowl to cool down.
Once cooled, use a large ice cream scoop to portion out the filling (8) onto a plate.
Cover the plate with plastic wrap and place into the fridge to chill for at least 1-2 hours.
Make the tangzhong:
In a small saucepot, add in flour and water.
Whisk over low-medium heat for about 3-4 minutes, until thickened, like a paste. Remove from heat and let cool to room temperature.
Make the dough:
Pour the warmed milk into a bowl, add in the sugar and yeast.
Give it a stir and let the yeast activate and bubble.
In a bowl of a stand mixer fitted with a dough hook, add in the flour, 40g egg (remember to save some for the eggwash later), oil and sea salt.
Start the mixer on low and pour in the activated yeast and milk. Add in the cooled tangzhong.
Knead until the dough starts to come together and forms a smooth and shiny ball, about 7-8 minutes of kneading.
Put the dough into a lightly greased bowl and cover with plastic wrap. Place in a warm location and let the dough double in size (approximately 60-90 mins, depending on how warm your kitchen is).
Prepare a baking sheet with parchment paper. Set aside.
Once the dough has risen, deflate the dough and divide into equal portions, about 65g each.
Roll each portion of dough with a rolling pin into a circle about 5" in diameter, leaving the centre slightly raised and the edges thinner.
Using the ice cream scoop, transfer the portioned curry beef filling (appx 55-60g) to the centre of the dough and carefully gather the dough up around the filling, pinching the seams. Note: The amount of filling is quite a bit for the dough but it will all fit. You can also decrease the amount of filling to make more room to work with the dough.
Shape the bun, gently flatten it a little and place onto the baking sheet and repeat with the remainder.
Preheat oven to 375°F/191°C.
Cover the buns loosely with plastic wrap and leave to rise until slightly puffy, about 20-30 minutes. Note: You'll know the buns are perfectly proofed when you make a little indentation and it slowly fills back in. If the fills back in quickly, give it a little more time.
Brush the tops of each bun with the leftover beaten egg. Add a little black sesame seeds to the centre of the bun.
Bake at 375°F/191°C for 15-16 minutes, until lightly golden in colour, or until the dough reaches an internal temperature of 190°F/88°C.
Make the sugar glaze:
In a small bowl, add in the sugar and hot water and stir together to make a syrup.
Once the buns are done baking, remove them from the oven and brush the tops of the buns with the sugar syrup.
Turn the oven off and place the buns back into the oven for 2 more minutes.
Remove the buns and let cool slightly. Best served warm and fresh.