Sweet potato fries with harissa mayo

Peel and cut the sweet potatoes into 0.5cm-thin chips. Pour 5cm oil into a large saucepan (a deeper pan will prevent splashes) and bring up to frying temperature (180ºC) over a medium heat. Check the temperature by dropping in a small piece of bread – if it turns golden after about 30 seconds, it is ready.

Meanwhile, in a small bowl, combine the sumac and salt. In another small bowl, combine the harissa mayo ingredients and season. Fry the chips in the hot oil in batches, making sure not to overcrowd the pan; turn them occasionally to ensure all sides cook and brown evenly. Each batch will take 6-10 minutes, depending on the type of hob you have (gas tends to cook faster).

Once cooked, use a slotted spoon to carefully transfer the fries to a plate lined with kitchen paper. Sprinkle the sumac salt all over each batch while still hot, then serve with the mayo for dipping and wedges of lime alongside.