Prepare Your Jar and Onions: First, ensure you have a clean 500ml glass jar with a tight-fitting lid. Wash it thoroughly in hot, soapy water and rinse well. While it air-dries, prepare your onions. Peel them, slice off the top and root, and then cut them in half from pole to pole.

Slice the Onions: Using a very sharp knife or a mandoline (be careful!), slice the onion halves as thinly as you can. I aim for slices around 1-2mm thick. Uniformly thin slices will pickle more evenly.

Pack the Jar: Gently separate the onion slices into rings and pack them into your clean jar. Don't press them down too hard, but you want the jar to be quite full as they will settle a bit. If you're using any optional aromatics like garlic or peppercorns, add them now.

Make the Brine: In a small, non-reactive saucepan (stainless steel is ideal), combine the white wine vinegar, apple cider vinegar, water, caster sugar, and sea salt.

Heat the Brine: Place the saucepan over a medium heat. Stir occasionally until the sugar and salt have completely dissolved. You want the mixture to be hot and steaming, but there's no need to bring it to a rolling boil. This should take about 3-4 minutes.

Pour and Pickle: Carefully pour the hot brine directly over the onions in the jar, making sure they are fully submerged. You should see them start to turn a beautiful bright pink almost instantly. What works best for me is using a small funnel to avoid any spills.

Cool and Seal: Use a spoon to gently push down any onions sticking out of the liquid. Let the jar sit on the counter with the lid off for about 20-30 minutes to cool down slightly.

Refrigerate: Once cooled, screw the lid on tightly and place the jar in the refrigerator. They are ready to eat in as little as 30 minutes, but for the best flavour and texture, leave them for at least a few hours or, ideally, overnight.