Pajeon (Korean Scallion Pancake)

FOR THE SAUCE: Whisk all ingredients together in small bowl; set aside.

FOR THE PANCAKES: Line large plate with double layer of paper towels and set aside. Separate green tops of scallions from white and light green parts. Halve white and light green parts lengthwise. Cut all scallion parts into 2-inch lengths and set aside. Whisk flour, potato starch, sugar, baking powder, baking soda, pepper, and salt together in medium bowl. Add ice water and garlic and whisk until smooth. Using rubber spatula, fold in scallions until mixture is evenly combined.

 Heat 2 tablespoons oil in 10-inch nonstick or carbon-steel skillet over medium-high heat until just smoking. Stir batter to recombine. Run blade of spatula through center of batter to halve and scrape half of batter into center of skillet. Spread into round of even thickness, covering bottom of skillet, using spatula or tongs to move scallions as necessary so they are evenly distributed in single layer. Shake skillet to distribute oil beneath pancake and cook, adjusting heat as needed to maintain gentle sizzle (reduce heat if oil begins to smoke), until bubbles at center of pancake burst and leave holes in surface and underside is golden brown, 3 to 5 minutes. Flip pancake and press firmly into skillet with back of spatula to flatten. Add 1 tablespoon oil to edges of skillet and continue to cook, pressing pancake occasionally to flatten, until second side is spotty golden brown, 2 to 4 minutes longer. Transfer to prepared plate.

 Repeat with remaining 3 tablespoons oil and remaining batter. Drain second pancake on prepared plate for 2 minutes. Cut each pancake into 6 wedges and transfer to platter. Serve, passing sauce separately.