Preheat the oven to 200°F (95°C). Line a baking sheet with paper towels and place it in the oven to keep the pancakes warm between batches.

Make the dipping sauce by whisking together soy sauce, rice vinegar, chopped scallion whites, sesame oil, sugar, sesame seeds, and gochugaru if using. Set aside.

Prepare the batter by whisking together all-purpose flour, rice flour, salt, garlic powder, onion powder, and baking powder in a large bowl. Add water, egg, and sesame oil. Whisk until smooth and thin. The batter should be runny; add extra water 1 tablespoon at a time if needed. Let it rest while preparing the scallions.

Trim the root ends from the scallions. Cut into 3–4 inch pieces, then slice thicker parts lengthwise. Divide into 4 even portions.

Heat a large nonstick pan over medium-high heat. Add 2 tablespoons oil and spread 1 portion of scallions in a single layer. Pour about 1/2 cup batter evenly over the scallions.

Cook for 3–4 minutes until the bottom is golden and crispy. Flip carefully and cook another 3–4 minutes until browned and cooked through.

Transfer to the prepared baking sheet and keep warm in the oven. Repeat with remaining batter, adding a little oil before each batch.

Slice the Pajeon (Korean Scallion Pancakes) into wedges or squares and serve hot with dipping sauce.