Chop the cabbage into pieces roughly ¼ inch (5 mm) in size. Sprinkle it with salt, mix well, and let it sit for about 10 minutes. Then, squeeze out any excess moisture by hand.
Finely chop the garlic chives.
In a large bowl, combine the ground pork with the seasonings for the gyoza filling (grated garlic, grated ginger, sake, sugar, salt, soy sauce, ground black pepper, toasted sesame oil, and potato starch or cornstarch). Mix thoroughly until the mixture becomes sticky.
Add the cabbage and garlic chives to the pork mixture, and gently stir to combine. The gyoza filling is now ready.
Prepare the gyoza wrappers and a small bowl of water. Place a wrapper in the palm of your non-dominant hand, and scoop some gyoza filling (about 1 Tbsp; ideally, as much as the wrapper can hold without spilling out when folded) with a small spatula or spoon, and place it in the center of the wrapper. Then, dip the tip of your dominant index finger into the small bowl of water and lightly moisten the edge of the wrapper. Using the thumb and index finger (or middle finger) of your dominant hand, fold the wrapper and pleat the edges to seal the gyoza. Repeat until all the wrappers or filling are used up.For a detailed guide on pleating gyoza, see the “How to Wrap Gyoza” section above. Coat a pan with about ½ Tbsp of sesame oil, spreading it evenly. Arrange the gyoza in a row or in a circle with a little space between each, pressing them gently against the pan.Cook only as many gyoza as will comfortably fit in the pan at a time. I cooked mine in two batches, but the number of batches will vary depending on your pan size. Adjust the amount of sesame oil according to the size of your pan. Heat the pan over medium heat. Once the pan is hot, add enough hot water to come about one-fourth to one-fifth of the height of the gyoza. Cover with a lid and steam for about 4 minutes.
Remove the lid, and if any water remains in the pan, continue cooking until it has evaporated. Then, drizzle about ½ Tbsp of sesame oil over the gyoza and cook them for another 1-2 minutes, until the bottoms are golden brown and crispy. (Adjust the amount of sesame oil according to the size of your pan.)
Transfer the gyoza to a plate, crispy side up. Serve with dipping sauce on the side. Wipe the pan quickly with a paper towel, then cook the next batch of gyoza.