Preheat the oven to 110°C/gas mark ¼. Line two baking sheets with non-stick baking paper.
Using a mandolin slicer, cut the sweet potato into very thin slices. If you don’t have a mandolin, you can cut the potato into super-thin slices using your sharpest knife. Put in a mixing bowl and pour over the oil. Add a decent pinch of salt and mix well to coat all the crisps.
Put the potatoes on the lined baking sheets in a single layer. Bake in the oven for 1 to 1½ hours, until crisp, rotating the sheets halfway through. Allow the crisps to cool for 5 minutes before eating.
Store any leftovers in an airtight container for up to a week.