In a large mixing bowl, whisk together the 2 cups all-purpose flour and ½ tsp salt. Pour in the boiling water gradually while stirring with a fork or chopsticks. Once shaggy, use your hands to bring the dough together into a rough ball. The hot water creates a softer, more pliable dough — this is key.

Turn the dough out onto a lightly floured surface and knead for 5–7 minutes until smooth and elastic. It should feel like soft Play-Doh — not sticky, not stiff. Wrap tightly in plastic wrap and rest at room temperature for 30 minutes. This rest is non-negotiable for easy rolling.

Soak the 2 oz dried glass noodles (dangmyeon) soaked in hot water 10 minutes, drained, finely chopped in hot water for 10 minutes until softened. Drain well, then chop into small ½-inch pieces. Set aside. While they soak, press the 7 oz firm tofu excess water pressed out firmly between paper towels or a clean kitchen towel to remove as much moisture as possible, then crumble it into a mixing bowl.

Finely chop the 1 cup napa cabbage kimchi finely chopped and squeeze it firmly in your fist over the sink to remove excess liquid. This step is critical — too much moisture will make your filling soggy and your wrappers tear.

In a large mixing bowl, combine the ½ lb ground pork, crumbled 7 oz firm tofu excess water pressed out, chopped napa cabbage kimchi finely chopped, chopped dried glass noodles (dangmyeon) soaked in hot water 10 minutes, drained, finely chopped, 3 stalks green onions finely chopped, 4 cloves garlic minced, 1 tsp fresh ginger grated, 2 tbsp soy sauce, 1 tbsp sesame oil, 1 tsp sugar, ¼ tsp black pepper freshly ground, and 1 egg. Mix thoroughly with your hands until everything is evenly combined and the mixture feels cohesive. Taste a small pinch — it should be well-seasoned and savory. Adjust 2 tbsp soy sauce or 1 tbsp sesame oil as needed.

Stir together the 2 tbsp soy sauce, 1 tbsp rice vinegar, 1 tbsp sesame oil, 1 tsp sugar, 1 tsp gochugaru (if using), and sliced stalks green onions finely chopped in a small mixing bowl until the 1 tsp sugar dissolves. Set aside.

Divide the rested dough in half. On a lightly floured surface, roll one half into a thin log about 1 inch in diameter, then cut into 20 equal pieces. Keep the other half covered. Flatten each piece into a disk with your palm, then roll each disk into a round about 3½ inches in diameter — thin edges, slightly thicker center. Work in batches and keep finished wrappers covered with a damp cloth.

Place a wrapper in your palm. Scoop about 1 heaping teaspoon of filling into the center — don't overfill or the edges won't seal. Lightly wet the edge of the wrapper with a dab of boiling water just-boiled using your fingertip. Fold the wrapper in half over the filling to form a half-moon. Press the edges firmly together, then crimp by folding and pinching small pleats along the sealed edge. Press down firmly to seal — any gaps will cause them to burst during cooking. Place finished mandu on a lightly floured tray. Repeat with remaining dough and filling.

Heat a large non-stick or cast iron skillet over medium-high heat. Add the 2 tbsp neutral oil such as vegetable and swirl to coat. Once shimmering, arrange mandu flat-side down in a single layer without crowding (cook in batches if needed). Fry undisturbed for 2–3 minutes until the bottoms are deep golden brown.

Carefully pour the ¾ cup boiling water just-boiled into the cast iron skillet (it will splatter — stand back!). Immediately cover with a tight-fitting lid. Steam for 5–6 minutes until the ¾ cup boiling water just-boiled has evaporated and the wrappers look translucent and cooked through. Remove the lid and let any remaining moisture cook off for 1 minute so the bottoms re-crisp.

Transfer the mandu golden-side up to a serving plate. Serve immediately with the dipping sauce on the side. They're best eaten hot, right out of the pan.