Steam the sweet potatoes: Peel and slice them into thick rounds. Steam over boiling water for 15–20 minutes, until a chopstick goes through easily.

Mash and mix: While still hot, mash the steamed sweet potato. Mix in sugar and condensed milk. If too dry, gradually add milk in 2–3 additions (5–10ml each) until smooth and moldable like thick mashed potatoes.

Cool: Let the filling cool to room temperature before using.

Mix ingredients: In a large bowl, combine flour, sugar, and yeast. Add lard, then pour in warm water. Stir with chopsticks until shaggy.

Knead: Knead by hand for 5–8 minutes into a smooth dough. If sticky, dust lightly with flour—but add only a little to keep it soft.

Divide dough: Cut into 8–10 equal pieces (each about 40–50g).

Roll and fill:

Roll one piece into a ball, then flatten into an 8–10cm round wrapper (edges slightly thinner).

Place 25g filling in the center, pinch closed like a bun, then gently flatten.

Roll into a tongue shape (12–15cm long, 6–8cm wide).

Cut and roll into spirals:

Cut evenly spaced strips across the surface (don't cut through).

Flip over, press one edge thinner, roll up from the other end.

Pinch both ends to seal into a spiral.

Rise: Place shaped rolls on a steamer lined with oil or parchment, leaving 2cm space between each. Cover and proof at room temperature for 30 minutes (in winter, add warm water to the steamer to help proof). They're ready when puffy and bounce back slowly when pressed.

Steam:

Start from cold water. Bring to a boil on high heat, then steam over medium for 15 minutes.

Turn off heat and let sit for 3 minutes before opening the lid (prevents shrinking).