Make the Brine - In a small saucepan, combine the white wine vinegar, water, brown sugar, salt, peppercorns and bay leaves. Bring to a gentle simmer over medium heat, stirring until the sugar dissolves.

Slice Onions - Thinly slice the red onion with a sharp knife. Place the sliced red onions in a sterilized glass jar or heatproof bowl.

Combine and Cool - Pour the hot vinegar mixture over the onions, ensuring they are fully submerged. Allow to cool to room temperature, then seal and refrigerate for at least 1 hour before serving.

Storage Instructions - The pickled onions will keep in the fridge for up to 2 weeks.