Heat the oven well. Peel the potatoes, wash and cut them into uneven pieces.
Put them to blanch in boiling water for 5 min. Drain them and lay them out onto paper towels to cool.
Mix the potatoes with the oil and butter in an oven dish. Sprinkle with salt and put them to bake in the oven for about 1 hour or until softened.
Optionally, you can add spices of your choice to the potatoes prepared in this way.