01 -
Peel the red onion and slice it thinly. You can slice into rings, half-moons, or dice depending on how you plan to use them. Set aside while you prepare the pickling liquid.
02 -
In a clean preserve jar or container with a tight-fitting lid, combine the white wine vinegar (or apple cider vinegar), caster sugar, salt, and wholegrain mustard.
03 -
Secure the lid on the jar and shake well to fully dissolve the sugar and salt in the vinegar. This creates your pickling brine.
04 -
Add the sliced onions to the jar containing the pickling liquid. Make sure all the onion slices are submerged in the brine. Give it another good shake or stir to coat evenly.
05 -
Place the jar in the refrigerator and let the onions pickle for at least one hour before using. They will turn a beautiful pink color as they soak up the brine.
06 -
Keep the pickled onions refrigerated. They'll be ready to use after an hour but will develop more flavor over time. They can be stored in the refrigerator for up to 2 weeks.