Chinese Pork Potstickers

3 cups minced napa cabbage leaves
3/4 teaspoon table salt
3/4 pound ground pork
4 minced scallions (about 6 tablespoons)
2 egg whites, lightly beaten
4 tsp soy sauce
1 12/ tsp minced or grated fresh ginger
1 medium garlic clove, minced
1/8 tsp ground black pepper
1 package round gyoza wrappers
2 Tbl vegetable oil
1 cup water

1. For the filling:: Toss cabbage with the salt in colander set over a bowl and let stand until cabbage begins to wilt, about 20 minutes. Press the cabbage gently with rubber spatula to squeeze out any excess moisture, the transfer to a medium bowl. Add the remaining filling ingredients and mix thoroughly to combine. Cover with plastic wrap and refrigerate until mixture is cold, at least 30 minutes or up to 24 hours.
2. For the dumplings: Working with 4 wrappers at a time (keep the remaining wrappers covered with plastic wrap), fill each dumpling using a generous 1 teaspoon of the chilled filling per dumpling. Brush the edge with a bit of water and fold in half to make a semi-circle. Pinch each dumpling closed, pressing out any air pockets. Transfer the dumplings to a baking sheet and repeat with the remaining wrappers and filling. (The dumplings can be wrapped tightly with plastic wrap and refrigerated for up to 1 day, or frozen for up to 1 month. Once frozen, the dumplings can be transferred to a zipper-lock bag to save space in the freezer; do not thaw before cooking.)
3. Line a large plate with a double layer of paper towels; set aside. Brush 1 tablespoon of the oil over the bottom of a 12-inch nonstick skillet and arrange half of the dumplings in the skillet, with a flat side facing down (overlapping just slightly if necessary). Place the skillet over medium-high heat and cook the dumplings, without moving, until golden brown on the bottom, about 5 minutes.
4. Reduce the heat to low, add 1⁄2 cup of the water, and cover immediately. Continue to cook, covered, until most of the water is absorbed and the wrappers are slightly translucent, about 10 minutes. Uncover the skillet, increase the heat to medium-high, and continue to cook, without stirring, until the dumpling bottoms are well browned and crisp, 3 to 4 minutes more. Slide the dumplings onto the paper towel-lined plate, browned side facing down, and let drain briefly. Transfer the dumplings to a serving platter and serve with soy sauce for dipping.