How to Make It
Preheat the oven to 425°. Using a sharp paring knife, slice each potato crosswise at 1/4-inch intervals, cutting straight down but not all the way through the potato. Transfer the potatoes to a large cast-iron skillet.
Add the butter to the skillet and set over moderate heat; as the butter melts, spoon it over the potatoes. Season the potatoes with salt and transfer to the oven. Roast for about 40 minutes, basting occasionally, until golden and tender. Sprinkle the breadcrumbs over the potatoes and roast for 10 minutes longer, until golden and crisp. Serve hot.