Place a baking tray in the oven and preheat it to 230 degrees C (450 degrees F).
Parboil the potato chips, skin on, for about 10 minutes in boiling salted water.
Heat some olive oil in a frying pan, smash the garlic bulb and chuck in the cloves, then add the potato chips. Toss in the oil and season with pepper. Bake on the preheated tray for 15 to 20 minutes until crispy and golden.
Remove the leaves from the rosemary and put in the mortar with the lemon zest and salt. Bash up to make a green paste, adding more salt if it is too wet. Push through a sieve, and sprinkle on the chips to serve.