Peel the potatoes and cut them into even sized pieces (about 3 cm).
Bring a large pot of lightly salted water to a boil.
Preheat the oven to 200° C.
Cook the potatoes for 5-7 minutes. They should not be fully cooked.
Drain the water, then put the lid on the pot and shake the potatoes vigourously for a few seconds until their surface has become roughened.
Evenly spread 3 Tbsp of olive oil on your oven sheet and place sheet in the hot oven for 1-2 minutes.
Take hot sheet out of the oven and distribute the cooked potato pieces on it. Carefully toss them so they are lightly coated oil on all sides. Then make sure to spread them out on the sheet so they touch each other as little as possible.
Bake for 30 - 40 minutes until they are golden brown. Turn them every 10 minutes.