Preheat oven to 475°F.
Cut a thin slice off the bottom of each potato so they lay flat.
Using a sharp knife, make 20–30 thin slices lengthwise across the top of each potato, about ¼ inch apart, leaving about ½ inch at the bottom intact. Don't cut all the way through!
Mix the melted butter and oil in a bowl.
Place the potatoes on a baking sheet, brush with half of the olive oil/ butter mixture, sprinkle with salt and bake for 30 minutes.
Brush the potatoes with the remaining oil/butter mixture and cook for an additional 30-45 minutes or until skin is golden and serve.
