Ingredients

• 1/4 medium white onion, thinly sliced
• 1 bunch scallions, julienned
• 1 tablespoon gochugaru (Korean red pepper powder)
• 1 tablespoon sugar
• 1 teaspoon kosher salt, plus more
• 1/2 teaspoon freshly ground black pepper, plus more
• 1 teaspoon distilled white vinegar

Instructions

1. Place onion and scallions in a medium bowl of cold water. Chill until scallions curl, at least 20 minutes.
2. Meanwhile, whisk gochugaru, sugar, 1 teaspoon salt, 1/2 teaspoon pepper, and 1 tablespoon water in a medium bowl. Let sit, whisking occasionally, until sugar is dissolved and sauce looks shiny, about 10 minutes.
3. Drain onion and scallions and spin in a salad spinner or pat dry. Transfer to bowl with gochugaru sauce. Add vinegar and toss to coat; season with salt and pepper.
4. Do ahead: Onion and scallions can be soaked 1 day ahead. Keep chilled.