Heat a large non-stick frying pan over a medium heat. Add the sliced onion with a pinch of salt and cook for 5-10 mins, stirring regularly, until beginning to soften and develop some colour. Reduce the heat to medium-low and continue cooking for another 20-25 mins, stirring occasionally, until beautifully soft and golden. If the onion begins to catch, add a splash of water and scrape up any caramelised bits from the bottom of the pan. Once ready, transfer to a plate and set aside.