Position oven rack in the center and preheat to 400°F/200°C.

Slice the potatoes as thin as possible, 1/8 inch (0.3 cm). Using a mandoline is the best way to get the thinnest, even slices.

Spread out onto a clean towel and pat dry.

To a small saucepan add the butter, rosemary, salt and pepper and heat until the butter is melted.

Add the potatoes to a large mixing bowl and pour over the melted butter, rosemary and salt. Mix well until all the potatoes are coated.

To a small baking dish (about 8 inch square), line the potatoes vertically.

Sprinkle with a little more salt and bake for 45-60 minutes or until the potatoes are tender. To test use a skewer or thin sharp knife to test that the potatoes are cooked in the center. If they start to brown too much on the top, cover with foil.