This dumpling recipe uses gat kimchi as its filling for bright flavor in every bite. Be sure to cook the kimchi in Step 2 until almost no liquid remains—a watery filling can mean soggy wrappers and broken dumplings. Read more about this recipe.
To prepare dumplings: Soak shiitakes in a bowl of warm water for 15 minutes. Drain and squeeze out excess water. Remove and discard stems. Chop caps finely.
Heat canola (or avocado) oil in a wok or large skillet over medium-high heat. Add onion and cook, stirring often, until softened and just starting to brown at the edges, about 1 minute. Add the shiitakes and cook, stirring occasionally, until dried and tender, about 2 minutes. Add kimchi and cook, stirring often, until the moisture has evaporated, about 2 minutes. Remove from heat and let cool for 10 minutes.
Combine pork, finely chopped scallions, garlic, ginger, 1 teaspoon sesame oil, 1 teaspoon soy sauce, sugar, salt and pepper in a medium bowl. Add the kimchi mixture and mix until evenly distributed.
Put a large pot of water on to boil. Line 2 baking sheets with parchment paper and dust generously with flour.
Spoon about 1 heaping tablespoon filling in the center of a wrapper. Dip a finger in a small bowl of water to wet the edges of the wrapper. Fold over and firmly seal. Pleat the edges, if desired. Repeat with the remaining wrappers and filling. Place the dumplings on the prepared pans and cover with a slightly damp kitchen towel.
Adjust heat so the water is at a gentle boil. Carefully add half the dumplings and gently stir so they don't stick to the bottom. Cook until they float to the surface and the wrappers are tender, 6 to 8 minutes. Using a slotted spoon and letting excess water drip back into the pot, transfer the dumplings to a serving platter and cover to keep warm. Repeat with the remaining dumplings.
Meanwhile, prepare sauce: Mix soy sauce, vinegar, water, sesame oil and sliced scallion along with red chile and sesame seeds to taste in a small bowl. Serve with the dumplings.
Freeze uncooked dumplings (Steps 1-5) in a single layer on a baking sheet, then transfer to a sealable plastic bag and freeze for up to 1 month. Cook from frozen.