Haemul Pajeon (Seafood Pancakes)

Stir 3 Tbsp. soy sauce, 2 Tbsp. unseasoned rice vinegar or apple cider vinegar, and 1 tsp. sugar in a small bowl until sugar is dissolved. Add ¼ small onion, coarsely chopped, 1 scallion, chopped, and 1 small red chile, thinly sliced, and mix to combine. Set sauce aside.

Place a wire rack inside a parchment-lined rimmed baking sheet. Whisk 1 cup (125 g) all-purpose flour, 3 Tbsp. potato starch or cornstarch, ½ tsp. baking powder, and ¼ tsp. freshly ground black pepper in a large bowl. Gradually pour in 1⅓ cups cold water, whisking constantly until just combined. Add 2 bunches scallions, cut into 2" pieces, white parts halved lengthwise if thick, and 1 cup frozen mixed seafood, thawed, drained, patted dry, cut into bite-size pieces; mix with a rubber spatula or wooden spoon to coat.

Heat 3 Tbsp. vegetable oil (you want enough oil to cover the surface generously, so add more if needed) in a large skillet, preferably nonstick (add a bit more oil if using stainless steel), over medium-high heat until hot but not smoking. Ladle half of batter into pan and carefully but quickly spread into a round (the ladle or spatula will do the job; you just want to make sure the pancake is not too thick). Scatter half of 1 small red chile, thinly sliced, over and cook pancake, reducing heat if browning too quickly, until golden underneath, 2–3 minutes. Using a metal spatula, carefully flip pancake over and pour in up to 1 Tbsp. more vegetable oil around perimeter; cook until other side is golden, 2–3 minutes. If you want your pancake extra crispy, flip again and continue to cook, flipping halfway through and adding a little more oil if needed, 2 minutes longer. Transfer pancake to wire rack. Repeat with remaining batter, remaining half of 1 small red chile, thinly sliced, and more oil to make another pancake.

Cut pancakes into squares or wedges if desired and arrange on plates. Serve with sauce alongside for dipping.