Step 1 (Make Dough): In a bowl, mix 2.5 cups flour with 1 cup warm water (50°C/120°F). Knead for 8-10 minutes until smooth and elastic. Cover with a damp cloth and rest for 30 minutes (critical for gluten relaxation and easy rolling).
Step 2 (Prep Cabbage): Toss 200g chopped cabbage with 1/2 tsp salt. Let sit for 15 minutes. Squeeze firmly in a clean cloth to remove all excess water (this prevents soggy filling).
Step 3 (Mix Filling): In a bowl, combine pork, cabbage, green onions, ginger, 2 tbsp soy sauce, 1 tbsp sesame oil, 1 tsp salt, 1/2 tsp white pepper. Stir vigorously in one direction for 3-4 minutes until mixture is sticky and cohesive.
Step 4 (Roll Wrappers): Divide dough into 40 pieces. Roll each into a 3-inch circle, keeping the center slightly thicker than edges (helps prevent bursting when sealing). Cover unused dough.
Step 5 (Fill & Pleat): Place 1 tbsp filling in center. Fold wrapper in half, pinch center. Using your thumb and index finger, make 3-4 pleats on each side, pressing firmly to seal (ensure no air pockets). Place on a floured tray.
Step 6 (Cook): TO BOIL: Bring a large pot of water to rolling boil. Add dumplings in batches. Stir gently. When water returns to boil, add 1 cup cold water. Repeat twice (three boils total). Dumplings are done when they float and wrappers are slightly translucent, about 8-10 minutes. TO PAN-FRY: Heat 2 tbsp oil in non-stick skillet over medium-high. Arrange dumplings flat-side down. Cook for 3 minutes until golden brown. Add 1/2 cup water, cover immediately, reduce heat to medium. Steam for 6-7 minutes until water evaporates. Uncover, cook 1 more minute to crisp.
Step 7 (Serve & Store): Serve hot with black vinegar and chili oil. Uncooked dumplings can be frozen on a tray, then transferred to a bag for 3 months. Cook from frozen, adding 2 extra minutes to boiling time. Cooked leftovers refrigerate for 2 days; reheat by pan-frying.