Preheat the oven to 450°F (230°C/Gas Mark 8) and boil a kettle of water.
Scrub the potatoes and put in a large saucepan. Cover with boiling water, and boil gently for 5 minutes.
Pour the olive oil into a large, shallow roasting pan and put it into the oven to heat.
Wash the lemon and finely grate the rind. Rinse the rosemary leaves.
Drain the potatoes well. Remove roasting pan from oven and place potatoes into the hot oil and stir well to coat evenly. Make sure the oil is really hot before you begin roasting the potatoes should start to sizzle as soon as you put them into the pan. Sprinkle the lemon rind, rosemary leaves, and some salt and black pepper over them.
Roast the potatoes on the top rack of the oven for 20 minutes, until golden.