Select firm, small onions. Peel and trim the ends.
If using shallots or larger onions, slice them into uniform pieces.
Soak in a saltwater solution for at least an hour to enhance crispness.
Combine vinegar with water and sugar in a pot, adding preferred pickling spices.
Common spices include mustard seeds, coriander seeds, and peppercorns.
Bring to a gentle boil, stirring to dissolve sugar completely. Allow to cool slightly.
Place prepared onions into sterilized jars, packing tightly with enough room for the brine.
Pour cooled brine over onions, ensuring they are fully submerged.
Seal jars and store in a cool, dark place for at least two weeks for flavors to meld.