At least 24 hours before making the roast potatoes, infuse the oil. Pour the oil into a jug, roughly chop the herbs and garlic, put in to the oil and cover with clingfilm. Leave as long as you can so that the flavours infuse.
Pre-heat the oven to 220ºc / 430ºf
Clean the potatoes (leave the skin on) and then chop into quarters. Put into a saucepan and top up with cold water so that the potatoes are covered, add a good pinch of salt and put on to a high heat. Bring the potatoes to the boil and cook for a further 20-30mins until the potatoes have softened. You want them to hold their shape, but you should be able to pierce them with a fork. when they are ready, drain and leave them to one side.
Pour the infused oil into a oven proof dish and put in the oven. You want to get the oil really hot here, so give it a good 10 minutes to heat up.
Carefully (and I can not stress that enough - the oil is really hot!), remove the oil from the oven and gently put in the potatoes. Take a fork, and gently press down on each potato, a smash, rather than a mash. Pop the diced butter around the dish, give a really generous sprinkle of black pepper and then top with parmesan. Put back in the oven.
After 30 minutes, carefully remove the dish and gently turn over the potatoes, and pop back in the oven for another 30mins.
Once they are brown and crispy, remove from the oven. Take the potatoes out with a slotted spoon and let them rest on some kitchen towel.
Pop in a serving bowl, sprinkle over some salt and pepper and serve to the table.