In the KitchenAid mixing bowl, add 500 grams of all-purpose flour and 2 tsp of baking powder. Use a spatula and give them a rough mix. Add 2 tbsp of sugar and 2 tsp of yeast into 300 grams of whole milk. Stir to make sure the sugar is dissolved and the yeast should be well distributed. Pour the liquid into the flour. Use a spatula, quickly give it a premix.
Set the Kitchenaid at 4th speed. Let it run for 10 minutes.
10 minutes later, the dough should have a nice elastic looking. Take it out and knead it on the working surface. The machine already did most of the job. You just need less than a minute to make it into a round smooth dough. Cover it, let it rest for 10 minutes.
Flatten it with your hands first. Roll it into a 15*18 inches rectangle sheet. The thickness should be about 1/4 of an inch. Divide the sheet into 2 even pieces. Cover one half with a plastic wrap so it doesn’t get dry while you are working with the other piece.
Make the scallion flavor rolls. Drizzle 2-3 tsp of toasted sesame oil on the sheet. Apply it evenly. Sprinkle some Jiao Yan and diced scallion.
Roughly eyeball 2 straight lines. This divides the sheet into 3 even parts, lengthwise. Then fold it over. Pack it tight. Fold it again and press it down.
Put it on a cutting board. Divide this into 12 even parts. Pile 2 pieces together. Use a chopstick to press it right in the middle. Then hold 2 sides and pull it a little bit. Make a twist. Bend it around your forefinger. Pinch 2 ends and connect them together. You just keep doing that until finished.
Add some warm water to the steamer. It will help the proofing. Place all the scallion rolls in. Use parchment paper or apply some oil on the rack to prevent sticking. Leave some space between them because they will grow bigger. Put on the lid. Let it proof for 1.5 hours.
Quickly make the sesame roll because you want them to have almost the same amount of proofing time. Brush some room temperature butter onto the sheet. Sprinkle the sesame sugar powder. Even it out. Same as before, fold the sheet twice, lengthwise. Pack it tight. Divide it into 12 even pieces as well.
Pile 2 pieces together. Use a chopstick to press it down in the middle. Hold 2 sides and pull it. You don’t need to make a twist here. Just bend it. Put the chopstick right through the curve. Make a twist and then press the chopstick down against the cutting board. Pull it out. Keep doing that to finish the rest of the Hua Juan.
Put the sesame roll in the steamer. Continue proofing for 1 hour and 20 minutes.
Turn the heat to high. When the water comes to a boil. Let it continue steaming for 15 minutes.
15 minutes later, turn off the heat. Do not open the lid. Let it sit for another 5 minutes. Then you can enjoy it!