Heat the oil in a large deep frying pan over a low heat.

Add the onions with a generous pinch of salt and cook slowly for 30-40 mins. Stir occasionally to prevent them from sticking or burning until they become soft and golden. If the onions start to catch, add a splash of water to the pan and mix well.

Add the sugar and vinegar to give them a sweet, slightly sharp chutney flavour. Keep cooking on a low heat for another 5 mins, stirring occasionally until the mix is sticky, the sugar has dissolved and the vinegar has reduced. The onions are now ready to serve, or use in a recipe.