Combine 50g all-purpose flour and 200g glutinous rice flour in a large bowl, mixing them well with chopsticks. Gradually add 200g warm water while stirring with chopsticks. Continue stirring until the mixture forms a crumbly texture, with no dry flour visible.

Knead the mixture into a smooth dough with your hands. If the dough is too sticky, sprinkle a small amount of dry flour to adjust its texture, but avoid adding too much, as it may make the dough too stiff.

Once kneaded, cover the dough with plastic wrap and let it rest for 10 minutes. This will allow the dough to relax and become easier to work with.

Wash, peel, and slice 400g purple sweet potato into thin, even pieces. Thinner slices will cook faster and more evenly.

Steam the purple sweet potato slices on high heat for 15-20 minutes, or until a chopstick can easily pierce the slices.

Transfer the steamed sweet potato slices into a bowl. While still hot, add 20g white sugar and 50g whole milk. Use a spoon or rolling pin to mash the sweet potato into a smooth paste. If needed, you can add a bit more milk to adjust the consistency, but avoid making it too runny.

Roll the mixture into 12 filling balls.

Once the dough has rested, take it out and place it on a work surface lightly dusted with flour. Knead the dough briefly.

Roll the dough into a long strip, then divide it into small portions, each weighing about 30-40g. Roll each portion into a ball and flatten it into a round disc with a rolling pin. Aim for a thickness that's thicker in the center and thinner at the edges.

Scoop a spoonful of the purple sweet potato filling into the center of each dough disc. Slowly fold the edges up and pinch them tightly to seal the filling inside. Once sealed, gently press the ball into a round pancake shape with the seam facing down.

Preheat a flat pan or electric griddle and lightly brush the bottom with cooking oil. Once the oil is hot, add the prepared purple sweet potato cakes to the pan. Fry on medium-low heat to avoid burning the cakes.

Turn the cakes occasionally to ensure even cooking. After about 2-3 minutes, the first side will turn golden brown. Flip the cake over and continue frying the other side.

Once both sides are golden and the cakes feel firm and slightly elastic when pressed, remove them from the pan. Serve them warm, optionally garnished with toasted sesame seeds.