Heat oven to 200C/180C fan/gas 6.
Heat the oil in a large roasting tin in the
oven. Cut any larger potatoes in half.
Cover the potatoes in cold salted
water, bring up to the boil and cook
for 2 mins. Drain and steam-dry in
a colander for 5 mins, then shake
to ruffle up the outsides.
Remove the roasting tin – be really
careful as the oil will be hot. Tip in the
potatoes and garlic (if using), and use
a spoon to turn them so they are all
coated in the oil. Sprinkle with sea salt
and pepper, and roast for 1 hr 45 mins,
turning every 30 mins or so, until really
crisp and golden.