Thinly slice red onion (you’ll need one cup)using a sharp knife or mandolin.
Place the vinegar, water, salt, sugar and optional whole spices in a small pot on the stove and bring to a boil.
Add the sliced red onions and simmer for 30-60 seconds, stirring.
Turn off the heat and let this cool completely.
Place in a clean mason jar and store in the fridge for up to 3 weeks.
