Preheat the oven to 400°F. Wash the potatoes but do not peel. Place a wooden spoon on either side of each potato. Use a sharp knife to make 1/4 inch slices along the whole potato - the wooden spoon handles will prevent you from cutting all the way through. You will need to make shallow slices at the ends of each potato. Repeat with the remaining potatoes.
Place the potatoes with the cut side up on a baking sheet. Drizzle the potatoes with the melted goose fat. Use your fingers to gently separate the slices to allow a little of the fat to drip between the layers. Sprinkle generously with kosher salt.
Roast the potatoes for 30 minutes. Take the potatoes out and drizzle the slices with a little more of the goose fat. If there is extra fat on the baking sheet, you can use that to spoon over the potatoes, or else add a bit more.
Continue roasting the potatoes until they are crispy on the outside and tender on the inside, another 30 to 40 minutes as needed. If the potatoes are still hard inside, continue roasting until they are tender. Baste with the goose fat once or twice more if desired.
Season with a bit more kosher salt if desired and enjoy!