Peel and slice red onion into thin slices. Place into a pint sized mason jar, or other glass, plastic, or ceramic container with a sealable lid.
In a small saucepan stir together vinegar, sugar, and salt. Add in 1 or more additional optional flavorings as desired. Bring to a boil, then remove from heat.
Pour mixture over onions in jar until full. Place the lid on and let cool to room temperature.
Place the lid on to seal and refrigerate
Recipe Notes
Adapted from The Stay at Home Chef (www.thestayathomechef.com)