Cook the potatoes in salted boiling water until very tender which will take around 25-30 minutes.
Drain.
Preheat the oven to 425F and line a baking tin with foil.
Transfer the potatoes to the lined baking tin and allow to cool for five minutes or so.
Using a potato masher, gently squash each potato keeping it intact but reducing the height to around half an inch in thickness.
Brush with olive oil and season with salt and pepper then roast in the oven for around 15 minutes. Turn the potatoes and repeat the process of brushing with olive oil and seasoning with salt and pepper than roasting for a further 15 minutes.
Mix the shredded parmesan and parsley together in a bowl, sprinkle over the potatoes and allow to roast for just a few minutes more until the cheese is melted