Grilled Flank Steak with Charred Sweet Onion Relish | America's Test Kitchen

Ingredients

• 1 flank steak (about 1 1/2 pounds)
• Salt and pepper
• 1 red onion , peeled and cut into 1/2-inch rounds (see note)
• 2 tablespoons vegetable oil
• 1/4 cup red wine vinegar
• 1/8 teaspoon cayenne pepper
• 3 tablespoons brown sugar
• 1 tablespoon chopped fresh parsley