01 - In a large mixing bowl, combine the ground beef, napa cabbage, onion, green onions, garlic, ginger, soy sauce, sesame oil, mirin, sugar, black pepper, and egg. Mix thoroughly until all ingredients are evenly incorporated and the mixture holds together.
02 - Place a dumpling wrapper in the palm of your hand. Spoon 1 rounded teaspoon of filling into the center. Moisten the wrapper edges with water, fold into a half-moon shape, and pinch firmly to seal, creating pleats along the edge if desired. Repeat with the remaining wrappers and filling.
03 - In a small saucepan, combine the gochujang, honey, soy sauce, rice vinegar, sesame oil, and minced garlic. Simmer over low heat for 2 to 3 minutes, stirring occasionally, until the glaze thickens slightly and becomes glossy. Remove from heat and set aside.
04 - Heat 1 tablespoon of vegetable oil in a large nonstick skillet over medium-high heat. Arrange the mandu in a single layer without overcrowding. Cook for 2 to 3 minutes until the bottoms develop a deep golden crust.
05 - Pour ¼ cup of water into the skillet and immediately cover with a lid. Steam for 3 to 4 minutes until the wrappers become translucent and the filling cooks through. Uncover and continue cooking for 1 to 2 minutes until the water fully evaporates and the bottoms regain their crispness.
06 - Transfer the cooked mandu to a serving platter. Drizzle or brush generously with the warm gochujang glaze. Sprinkle with toasted sesame seeds and serve immediately while crisp.