Peel and cut the purple sweet potato into small chunks. Steam over high heat for 15–20 minutes, until completely tender and easily pierced with chopsticks.

While still hot, mash the sweet potato with 20g sugar until very smooth and lump-free. Add the milk and mix well. Let the mixture cool until warm to the touch (below 40°C / 104°F).

Add 600g flour and 5g instant yeast directly into the warm purple sweet potato milk mixture. Stir with chopsticks until shaggy crumbs form.

Knead by hand for 5–8 minutes until the dough becomes smooth, soft, and no longer sticks to your hands or the bowl. If the dough feels too dry, add 1–2 tablespoons of water gradually.

Transfer the dough to a work surface. Roll it into a log and divide evenly into 7 portions (about 100–110g each).

Take each portion and knead it with your palm until the surface is smooth and round, with no visible creases.

Lightly oil the steamer or line it with damp cloth. Arrange the buns with space between them.

Let them rest at room temperature for 25–35 minutes, until they grow to about 1.5 times their original size. When gently pressed, the dough should spring back quickly without sticking.

Bring water to a full boil before placing the buns into the steamer. Steam over medium heat for 15 minutes.

Turn off the heat and let the buns rest inside the steamer for 3 minutes before opening the lid.