Prepare the Onions:
Peel the red onion and slice it thinly into rounds or half-moons. Place the slices in a clean glass jar or container.
Make the Brine:
In a medium saucepan, combine the vinegar, water, sugar, and salt.
Add optional spices like peppercorns, garlic, bay leaf, or red pepper flakes for extra flavor.
Heat the mixture over medium heat, stirring until the sugar and salt dissolve. Remove from heat.
Pickle the Onions:
Pour the hot brine over the onion slices in the jar, ensuring all onions are fully submerged.
Let the mixture cool to room temperature, then seal the jar with a lid.
Refrigerate:
Store the jar in the refrigerator for at least 1 hour before serving. For best flavor, allow the onions to pickle for 24 hours.
