Peel the potatoes and chop into roughly evenly sized pieces
Add to a large pan filled with water and a generous punch of salt
Par boil for 7-10m minutes (a knife should be able to penetrate the potatoes around 1cm deep)
Preheat the oven to 220c and drain the potatoes
Let the potatoes cool for 5 minutes and shake them in the colander so the sides of the potatoes 'fluff up'
Add the oil to a large roasting tin and place in the oven (to heat up the oil) for around 5 minutes
Remove and immediately (but carefully) tip the potatoes in the oil (they should sizzle!)
Toss them in the oil so they're coated and liberally add your salt and pepper
Reduce the oven to 200c and roast the potatoes for 35 minutes
After 35 minutes, remove the tray and toss the potatoes around
Scatter the garlic cloves and rosemary sprigs on to the potatoes and drizzle a little more oil (if you wish)
Place them back in the oven for a further 25 minutes - leave them longer if required until golden and crispy