Combine the potato starch, flour, salt, egg, and 1 tbsp water in a bowl and mix the batter well with a whisk.

Rinse the oysters in several changes of cold water and drain.

Put the oysters in a small bowl, add the salt, and mix and with a spoon. Let the oysters sit for 10 minutes; this will firm them up while seasoning them. Place a strainer over another bowl and drain the oysters. Discard the liquid.

Pat the oysters dry with paper towels and transfer to a bowl. Add the potato starch and gently mix by hand to coat. Add the oysters to the bowl of batter and gently mix with a spoon.

Heat a large nonstick skillet over medium heat. Add the vegetable oil and swirl to coat. Using a spoon, scoop up 1 or 2 oysters, along with some batter, and add to the skillet.

For the dipping sauce:

Combine the soy sauce, vinegar, and hot pepper flakes in a small bowl. Add the sesame seed and spring onion and serve.