Make a dipping sauce with soy sauce, rice vinegar, sesame seeds, and chopped onions. Add chili if desired.

Pat the seafood dry and cut any large pieces to bite size so they cook through quickly in the batter.

Trim the spring onions so they fit the diameter of your frying pan, splitting any thick whites lengthwise for even cooking.

In a bowl, whisk the flour with a pinch of salt, then stir in the egg and ice-cold water just until a pourable batter forms.

Fold the seafood into the batter, coating each piece lightly while keeping the mixture loose enough to flow.

Heat a generous slick of vegetable oil in a non-stick over medium-high heat until shimmering.

Lay the spring onions in the hot pan in a single layer, letting them sizzle for a moment so they begin to soften and char.

Pour the seafood batter evenly over the scallions, tilting the pan so the mixture spreads to the edges and forms one cohesive round pancake.

Cook undisturbed until the bottom is deeply golden and crisp, pressing gently with a spatula to ensure full contact with the pan.

Slide a wide spatula (or two) underneath and flip the pancake in one swift motion; add a touch more oil around the edges and cook the second side until crisp.

Transfer the pajeon to a cutting board, slice it into bite-size wedges, and serve immediately with the prepared soy-vinegar dipping sauce.