Wash the sweet potato and steam over high heat for 15–20 minutes, until easily pierced with chopsticks or a fork. Let cool slightly, peel off the skin, and mash into a smooth, lump-free puree. Allow it to cool completely.

Add 220g flour and 60g corn oil to the cooled sweet potato puree. Mix with chopsticks until a shaggy dough forms, then knead by hand for 3–5 minutes until smooth and non-sticky. The dough should be soft but hold its shape.

Place the dough inside a plastic bag and roll it out evenly to about 3mm thickness. Cut open one side of the bag to expose the surface. Brush evenly with egg yolk, then sprinkle with sesame seeds and gently press them in.

Cut the dough into strips about 8–10cm long and 1cm wide. Preheat the oven to 180°C (355°F). Arrange the strips on a baking tray lined with parchment paper, leaving space between each piece.

Bake in the middle rack at 180°C for about 20 minutes, until golden and crisp. Keep a close eye during the last 5 minutes to avoid over-browning. Transfer to a cooling rack—these will become even crispier as they cool.