Finely slice the red onions as evenly as possible - using a knife or a mandolin.
Place the white wine vinegar, water and sugar in a small saucepan.
Bring to the boil, then reduce to medium heat and simmer for 5 minutes until the sugar dissolves.
Turn the heat off.
Add the red onions to the saucepan and stir, ensuring all of the onions are covered.
Sit the onions in the vinegar for one hour, until cool.
Pour into a clean jar and cool completely before refrigerating.
Video
Notes
Nutrition - the nutrition is roughly per serving. The whole jar is roughly 120 calories.Scant Meaning - scant means just under ½ a cup of water. The equivalent is 7 tablespoons of water.