Thinly slice onions to desired thickness using a mandoline or a very sharp knife
Add onions to container you will use to pickle. I typically divide the onions between two 16 oz mason jars but you can use one large 32 oz jar
Add vinegar, sugar, salt, and lime juice (if using) to a glass measuring cup or bowl
Heat water on the stove. I use my teapot for this step. When the water is ready add 2 c of water to the vinegar, sugar, and salt
Stir well until the salt and sugar has disolved
Pour liquid over onions
Seal with a lid or lids and place in the refrigerator overnight
ENJOY!
Notes
Onions will stay good in the refrigerator for 1-2 weeks
For a little spice slice a fresh serano or jalapeño pepper and place in the jar with the onions before adding the liquid.