1. Peel the purple sweet potato, cut into cubes, steam it, and mash into puree.
2. Pour low-gluten flour, butter, and sugar into a bowl and knead them together, then pour in purple potato mash and knead into a dough.
3. Roll out into thick cakes and cut into wide strips.
4. Brush the surface with egg yolk, sprinkle with sesame seeds (black and white sesame seeds are fine), put in the oven at 170 degrees, 25-30 minutes.
