First, peel, cut, and wash potatoes.
Next, bring water to boil in a pot as you cut potatoes into about 4 to 6 cubes each.
Then, add potatoes into boiling water for about ten minutes.
Now, you want to preheat your oven to 220 degrees Celsius. In a sheet pan, add the butter and oil and put into the oven so the butter can melt.
Once you remove the parboiled potatoes, pour into a sieve and shuffle and moving the potatoes up and down until the potato gets flaky and crumby all around (it will have a shaven type look around the edges).
Then, pull out the sheet pan with the butter and oil, put the potatoes in it and, using a spatula, move potatoes around so that it’s all coated in the oil and butter mixture.
Next, spread the potatoes out flat, sprinkle salt and pepper to taste, and remove the leaves of 1 or 2 sprigs of rosemary off the stem and put them on the potatoes.
Finally, put the pan in the oven to bake for 45 min on 220 degrees Celsius until it gets nice and golden and crispy.