Heat the oven to 180C/fan 160C/gas 4. Toss the potatoes in a little olive oil and season. Arrange the chicken and potatoes in a large roasting dish, big enough to fit everything in one layer. Add the garlic, cut-side up and the sprigs of rosemary. Drizzle with more oil, then season the chicken with plenty of salt for a crisp skin.
Roast for around 1 hour, or until the chicken is cooked through, Turning potatoes occasionally. Serve straight from the roasting dish – good served with fresh peas and sweetcorn.