Halve the onions, peel them and cut them into the thinnest possible strips. Place the onion rings into one large or two small screw-top or canning jars.

Put vinegar, water, sugar and salt into a pot and heat over medium heat, stirring until the sugar has dissolved.

Carefully pour the vinegar mixture into the jars of onions until all the onion rings are covered by the liquid. Screw the lids on the jars and set aside for 30 minutes.

The pickled onions are ready when they have a vibrant pink color and are nice and soft. The pickled onions can be stored in the refrigerator for two weeks in a tightly sealed container.