Pre-heat the groundnut oil to 140°C. Parboil the potatoes in a large saucepan of boiling, salted water 6-8 minutes until just tender when pierced with a sharp knife.
Drain and cool. Pat dry and then blanch in the oil in batches for 4-5 minutes until they almost start to colour at the edges. Remove and drain on kitchen paper.
Increase the temperature of the oil to 190°C and cook again in batches until golden and crispy on the outside; usually 4-5 minutes. Remove and drain then season with salt. Serve immediately in large bowls.