White Dough: In a mixing bowl, combine the ingredients for the liquid mixture: milk, dry instant yeast, cooking oil, and sugar. In another mixing bowl, combine the dry ingredients: all-purpose flour, wheat starch/corn starch/rice flour. Mix the two bowls thoroughly to ensure even distribution. Then, gradually pour the liquid mixture into the dry mixture, stirring continuously until a dough forms. Knead the dough until smooth and elastic, then shape it into a large ball. Cover it with plastic wrap and let it rest for at least 15 minutes.

Brown Dough: Similar to the white dough, combine a bowl of wet ingredients (milk, instant yeast, cooking oil, sugar) and another bowl of dry ingredients (all-purpose flour, wheat starch/corn starch/rice flour, cocoa powder). Mix the two bowls together to form the brown dough, and knead it until smooth. Wrap the dough with plastic wrap and let it rest for at least 15 minutes.

Roll out the white dough thinly, to about 2-3mm thickness. Next, perform a letter fold (as shown in pic 2). Then, flip the dough (as shown in pic 3), and perform the second letter fold (as shown in pic 4). This step is crucial for creating a better and smoother rectangular sheet.

Repeat the same process with the brown dough.

From the two rectangles obtained in step 2, roll them again to create one white and one brown flat dough. Place the brown dough over the white one (as shown in pic 2), then trim the edges to form a rectangle (as shown in pic 3). Flatten the dough further using a rolling pin (as shown in pic 4).

Roll the dough tightly into a log, ensuring the edges are well sealed. Roll it slowly and evenly.

Cut the rolled dough into small pieces, dividing it evenly. Each piece should exhibit a clear white and brown spiral pattern.

Place the pieces on a parchment-lined tray, leaving some space between each piece. Cover the tray with a clean kitchen towel and let the mantou proof at room temperature for 1 to 1.5 hours, or until they double in size. Once proofed, steam the mantou over medium heat for about 15-20 minutes, or until they are cooked through.

Remove the mantou from the steamer and let them cool slightly before serving. Enjoy your delicious chocolate spiral mantou!