Heat the oven to 200C/180C fan/gas 6. Cook the potatoes in a pan of boiling salted water for 4-5 mins until just tender. The potatoes can be boiled up to 24 hrs ahead and chilled. Put the oil and butter in a shallow roasting tin and heat in the oven until the butter is sizzling. Carefully add the potatoes to the hot tin and roast for 30 mins.

Shake the tin, then continue to roast for 10-15 mins until golden and crisp all over. Toss through the parsley and spoon into a serving bowl, then scatter over the pork scratchings, if using, and serve.