175g Irish St Gall cheese, mature cheddar or gruyere, grated
600ml double cream
Heat oven to 180C/fan 160C/gas 4. Use a Japanese mandolin or sharp knife to slice the parsnips and potatoes very thinly. Layer the parsnips and potatoes in a shallow gratin dish, sprinkling some cheese and onion and a little drizzle of the cream over each layer, seasoning with salt and pepper as you go. The top layer should be potatoes and parsnips with a final sprinkling of cheese and drizzling of cream.
Cover with foil and bake in the oven for 2 hrs, alongside the pork. Remove the foil and continue to bake for 20 mins until golden. For a really golden brown top, finish under a hot grill if you like.