Preheat the oven to 200°C (Gas mark 6/390°F).
Wash and gently scrub the potatoes.
Bring a large saucepan of water to the boil, then add the potatoes. Bring it back to the boil, then boil for 10 minutes.
Whilst the potatoes are boiling, peel and finely chop the garlic.
After 10 minutes, drain the potatoes well – the dryer the better.
Tip the potatoes into a roasting tin. Using a potato masher, gently crush the potatoes – enough to make them split slightly whilst still holding their shape.
Drizzle over the the olive oil, then sprinkle over the garlic and rosemary. Try to get as much of the rosemary and garlic in the cracks of the potatoes as possible to ensure maximum flavour.
Roast the potatoes for 20-25 minutes until cooked through, golden brown and crispy.
Season with plenty of salt and pepper, then tip into a bowl and serve immediately.