Melt the butter in a saucepan or microwave, then let it stand for about 5 minutes so the milk solids settle. Skim off the foam, and carefully pour the clear golden butter through a small sieve into a jug. Discard the milky solids.

Preheat the oven to 400°F (200°C; 180°C fan). Brush the base of a 10-inch (26 cm) cast-iron skillet with 2 tablespoons of the clarified butter.

Peel the potatoes and slice them on a mandoline to about 1.5 mm thick. Sort the slices into small, medium, and large groups as you go. Do not soak them in water.

Set one medium slice in the center of the skillet, then spiral slices around it, overlapping each one by about three-quarters. Add a second spiral of larger slices around the first.

Brush or dab the layer generously with clarified butter, then season with one-third of the salt and white pepper. Repeat for two more layers.

Lay a round of parchment paper over the top. Bake for 70 minutes, then remove the paper and bake for 30 minutes more until the top is golden and crispy. Let it rest for 10 minutes before flipping onto a plate.