1 cup red wine vinegar
1 tablespoon kosher salt
1 teaspoon sugar
1 red onion, sliced into rings
1 fresh chile pepper, such as red Fresno or jalapeño, sliced
2 fresh bay leaves
1 teaspoon coriander seeds
In a medium saucepan, combine the vinegar and 1 cup water and bring to a bubble. Add the salt and sugar and stir to dissolve.
In a glass jar (or even a deli container), layer in the onion, chile, bay leaves, and coriander seeds. Pour the hot vinegar on top.
Allow to cool, then cover and refrigerate for at least 2 hours and up to 2 days before using.