- To make dough, combine flour and ⅛ teaspoon salt in a medium mixing bowl. Pour in ½ cup hot water while stirring to form into a dough. Lightly flour a work surface and knead dough out for 7-10 minutes to soften and smooth. Transfer dough back to bowl and cover with plastic wrap. Allow dough to set out at room temperature for 30 minutes.
- Place cabbage in a small bowl and add remaining sea salt. Toss gently and set aside for 10 minutes to draw out moisture.
- Combine mushrooms, scallions, and garlic in a small bowl. Use a clean kitchen towel to wring out cabbage over sink, removing excess liquid. Add cabbage to bowl with vegetables. Stir and set aside.
- Stir together soy sauce, sesame oil, cilantro, ginger, and chili flakes in another small bowl.
- Divide dough into 12 small balls. Sprinkle each ball with flour and roll out onto work surface using a rolling pin to form round discs.
- Fill each disc with 1 heaping teaspoon of filling mixture in the center. Fold ends up and pinch dough to seal. Set onto a parchment paper lined baking sheet.
- Heat 2 tablespoons of sesame oil in a medium skillet over medium heat for 2 minutes. Add dumplings to skillet and cook 4-5 minutes to lightly brown bottoms. Reduce heat to low and slowing add hot water to skillet, cover and cook an additional 7-8 minutes to steam dough through. Serve hot garnished with sesame seeds, remaining scallions and sauce for dipping.