Step 1

Slice the red onions as thin as you can. I use a mandoline.

Step 2

Stuff all the red onions in the jar of your choice. A bowl will work too.

Step 3

In a measuring cup, combine apple cider vinegar, salt, sugar, and warm water. Stir to dissolve the sugar and salt. Pour this pickling mixture over your sliced onions, making sure they are immersed in the liquid, and let them set for an hour. After an hour, cover and store in the fridge for up to three weeks.