Peel and cut the sweet potato into bite-sized pieces. Soak them in water for 5 minutes, then drain.

Cover the sweet potato with plastic wrap and microwave for 4–7 minutes until cooked. Adjust the time if needed.

Mash the hot sweet potato with sugar and butter. Gradually add milk in 2–3 portions and mix well.

Defrost the frozen pastry sheets and sprinkle flour to prevent sticking. Roll out to 3mm thickness.

Spread the sweet potato filling evenly on the pastry sheet, leaving a 1cm border.

Roll up the pastry sheet and cut into pieces.

Mix egg yolk with water. Place the pastry pieces on a baking tray with the cut side up and brush with the egg mixture.

Sprinkle black sesame seeds and bake in the oven until golden brown.