Add flour, sugar, salt, egg, condensed milk, tangzhong/water roux, and yeast mix to a large mixing bowl.
Start kneading by hand or a mixer with a dough hook. We start with a hand mixer with the dough hook on the slowest mode for 3-4 mins and then increase the speed to 1 level up to mix for another 10 mins. Or knead until a smooth dough formed.
Add the butter to the dough, and knead again until a smooth dough formed. It will take another 10 mins.
Cover and leave it in a warm place to prove for 45 mins, or until it doubles its size.
In the meantime, cut the green onion into small pieces. Set aside.
In the cake form, brush a layer of butter.
After the first proof, press out all the air and put it on a floured surface. Divide the dough into 5 pieces. Shape each of them into a small round ball. Cover with a cling film and leave them to rest for 10 mins.
Take out one of the dough balls, flatten it with a rolling pin into an oval shape.
Cut into stripes for half of the oval shape.
On the other side, add the green onion, a pinch of salt, and white pepper.
On the green onion side, fold the two outer edges of the dough towards the middle, and start rolling from the green onion side to the side with the stripes.
Repeat for all 5 dough balls, and put the product in the cake form - on the edge like a ring.
Cover the cake form and place it in a warm place for the second proof - around 30 mins.
Preheat the oven to 175°C.
Brush some egg wash on top. (Alternatively, you can use milk instead.)
Bake in the oven for around 18 mins.
Remove from the cake form to cool down.