Step 1

In a small saucepan, stir together the vinegar, water, salt and your desired amount of sweetener. Cook over medium-high heat until the mixture reaches a simmer. (Or alternately, you can heat the mixture in the microwave.)

Step 2

Place the thinly-sliced onions in a mason jar. Pour the hot vinegar mixture over the onions, screw on the lid, and shake the onions briefly until they are evenly coated with the vinegar mixture.

Step 3

Let the onions marinate for 30 minutes. (You may need to press the onions down with a spoon so that they are all submerged under the vinegar mixture.)

Step 4

Serve immediately, or refrigerate the onions in a sealed container for up to 2 weeks.