Step 1

In a small saucepan*, stir together the vinegar, salt and your desired amount of sweetener.  Cook over medium-high heat until the mixture reaches a simmer.

Step 2

Place the thinly-sliced onions in a small bowl or pint-sized mason jar.  Pour the hot vinegar mixture over the onions.  Stir until combined.  (Or if using a mason jar, place the lid on top and give the jar a quick shake.)  Let the onions marinate for 30 minutes.

Step 3

Serve immediately.  Or refrigerate in a sealed container for up to 2 weeks.