Add the fruit rinds to a large saucepan and cover with water. Make sure they are totally submerged – a plate can help to weigh them down. Bring everything to the boil, then reduce to a simmer and cook for 30 minutes, or until the rinds are just starting to soften. Drain and set the fruit aside to cool. Once cooled, use a spoon to remove any remaining flesh or white pith from the peel and discard. In a medium saucepan, combine the caster sugar with 250ml of water and bring to a simmer over a medium heat, until the sugar is dissolved and the liquid is gently bubbling. Add the rinds, stir to combine, then reduce the heat to low and simmer for 25 minutes, or until the rinds are soft and translucent. Then take the pan off the heat and leave to cool in the syrup. Preheat the oven to the lowest setting. Using tongs, transfer the rinds to a wire rack set over a baking tray, then place in the oven for 1 to 2 hours, so they dry out but are still malleable. Remove from the oven and toss in a little caster sugar. Store in an airtight container in the fridge and chop as needed. It’ll last for up to six weeks in the fridge.