Bring the brine to the boil. Add potatoes and bring back to the boil. Simmer, covered, for 45 minutes or until potatoes are cooked through.
When thoroughly cooked, remove potatoes and place in a colander. Let spuds cool, and any excess brine drain. Chill for 24 hours.
Slice potatoes. Toss in a bowl with the remaining ingredients. Stir till well combined, then cover with cling film and chill till serving.
In the US, an Idaho potato is used. The potato should be soft after boiled, not hard or lumpy. Choose the appropriate one. If you just finished a jar of pickled onions, you can substitute that remaining pickling solution for the white vinegar.
To make the brine, combine 2.5L water, 500ml white vinegar, 600g granulated sugar and 200g salt.