1. Fill a saucepan with water, cover with a lid and bring to the boil. Add a tablespoon of salt then boil the potatoes for 10 minutes, until just tender to the point of a sharp knife. Drain in a colander and allow to steam dry for a minute while you make the cheesy garlic butter.
2. In a bowl large enough to hold the potatoes, combine the melted butter, oil, cheddar, garlic, rosemary and all but a teaspoon of the chopped parsley. Season well with salt and pepper, then toss the potatoes in the mixture to coat. Reserve any flavoured butter left in the bowl.
3. Preheat the oven to 220C.
4. Tip the potatoes into a large roasting tray and use the base of a flat glass to press down on each potato to split their skins. Use a pastry brush to distribute any remaining butter over the potatoes.
5. Roast the potatoes in the oven for 20-22 minutes, until crisp and golden all over.
6. Serve alongside grilled meats, vegetables or white fish.