Steam or boil purple sweet potatoes until tender (about 15-20 minutes).
Mash potatoes while hot, then let cool completely.
Mix in sesame oil, garlic, ginger, five-spice powder, green onions, egg, and flour.
Season mixture with salt and white pepper.
Shape into 2-inch croquettes using the scoop.
Chill formed croquettes for 30 minutes.
Set up breading station: flour, beaten eggs, and panko.
Coat each croquette in flour, egg, then panko.
Heat oil to 350°F (175°C).
Fry in batches until golden brown (3-4 minutes).
Drain on wire rack and season immediately.
Mix all sauce ingredients and serve alongside croquettes.