Prepare the cabbage: Finely chop napa cabbage, mix with 1/2 tsp salt, and let sit for 10 minutes. Squeeze out as much excess water as possible using a clean kitchen towel.

Make the filling: In a large bowl, combine ground pork, squeezed cabbage, green onions, grated ginger, minced garlic, soy sauce, sesame oil, sake (if using), cornstarch, salt, and black pepper. Mix thoroughly until all ingredients are well combined.

Assemble the gyoza: Place one gyoza wrapper on your palm. Moisten half of the wrapper's edge with water. Place about 1 teaspoon of filling in the center. Fold the wrapper in half to form a crescent shape. Starting from one end, make small pleats along the moistened edge, pressing them firmly to the unmoistened side to seal. Repeat with remaining wrappers and filling.

Cook the gyoza: Heat 1 tablespoon of vegetable oil in a large non-stick skillet over medium-high heat. Arrange half of the gyoza in a single layer, ensuring they don't touch. Cook for 2-3 minutes until the bottoms are golden brown and crispy.

Steam the gyoza: Pour 1/4 cup of water into the skillet. Immediately cover with a lid and reduce heat to medium-low. Let steam for 5-7 minutes, or until the wrappers are translucent and the pork filling is cooked through.

Crisp and serve: Remove the lid and increase heat to medium-high. Cook for another 1-2 minutes, allowing any remaining water to evaporate and the bottoms to crisp up again. Transfer to a serving platter. Repeat with the remaining gyoza, adding more oil if needed. Serve hot with your favorite dipping sauce.