Step 1

Prep the Onions: Thinly slice the onions on a mandolin and place in a medium, heatproof bowl.

Step 2

Make Pickling Liquid: Combine sugar, vinegar, water, and salt in a small saucepan. Bring to a boil, whisking to dissolve sugar. Let simmer 5 minutes then pour hot pickling liquid over vegetables.

Step 3

Store: Cool to room temperature, cover, and refrigerate until cold. The onions may not be totally submerged in the pickling liquid at first but will wilt as they cool and eventually be covered.