Scrub, wash and dry the potatoes very well. Preferably do this step in advance.
Using a sharp knife cut slices in the potatoes but without cutting all the through the bottom. Do this step with care. You want all those slices to still be connected at the bottom.
Pour a drop of olive oil in your hand and gently rub each potato all over before placing on a parchment lined roasting dish or in a cast iron skillet for a crisp bottom. ( you can use a small brush for this step if you prefer)
Sprinkle all over with salt and red pepper flakes.
Bake the potatoes in the preheated oven for 30 minutes. Quickly brush with a thin layer of olive oil and continue baking for another 30 minutes or so depending on the size of the potatoes.
If you are looking for an extra crispy top make sure to transfer the potatoes under the broiler flames for a minute or so before serving.