Quick-pickled red onions in a sweet-tart brine of apple cider vinegar, white vinegar, sugar, and salt. A simple condiment for adding bright acidity and crunch.
Heat the vinegar, water, sugar, and salt in a medium saucepan over medium heat. Stir until the sugar and salt dissolve, about 1 minute. Let cool and pour over the onions. Store in the fridge.