Zest of one lemon
4 tablespoons sea salt
750ml vegetable oil
1kg potatoes, peeled and slices into thin fries
A few sprigs of rosemary
Make the lemon salt: in a mortar and pestle, bash together the lemon zest and salt until salt is coloured yellow and fine.
Heat 750ml of oil in a sturdy, high-sided pan and bring to deep-frying temperature. Tip: place a potato in the cold oil before you turn the burner on. When the potato rises to the top of the oil and begins to turn golden brown, the oil is ready. Remove the potato piece and start frying the potato fries in small batches until golden brown. Remove from oil with a slotted spoon, drain onto paper towel and then place in large bowl.
When you've finished frying all your potatoes, add the rosemary for the last 30 seconds.
Add rosemary to the bowl of fries and toss with the lemon salt. Serve immediately.