Preheat the oven to 450° F
Stir together the butter, olive oil, and some salt and pepper in a small bowl.
Place a potato between the handles of 2 wooden spoons or 2 chopsticks. Slice the potato into thin slices, leaving ¼ inch at the bottom unsliced; the spoon handles will prevent you from slicing the potato all the way through. Repeat with the remaining potatoes.
Put the potatoes on a baking sheet and brush on half of the butter mixture.
Bake 30 minutes. Brush on the remaining butter mixture, getting between the slices.
Bake 30--45 more minutes until tender and crisp.