Melt the butter in a saucepan or microwave. Set aside for 5 minutes until the milk solids settle on the bottom.
Scrape off the foam, then slowly pour the clear golden butter through a small sieve into a jug while leaving the milk solids behind.
Preheat oven to 200°C / 400°F (180°C fan-forced). Brush the base of a 24cm / 9.5" cast-iron skillet with 2 tablespoons of clarified butter.
Peel potatoes and using a mandolin, slice 2 or 3 potatoes 1.5mm / 0.6" thick. Quickly sort the slices into small, medium and large sizes. Do not put them in water.
Using the medium size slices, put one slice in the middle, then build a spiral around it, overlapping each slice by about ¾.
Using the larger slices, make a second spiral around the first one until the whole base is fully and evenly covered.
Brush / dab generously with clarified butter, taking care not to disturb or lift the slices. Season with a third of the salt and white pepper.
Repeat the same spiral pattern for 2 more layers, brushing with clarified butter and seasoning each layer.
Place a cartouche (circle of baking paper / parchment paper) on top.
Bake for 70 minutes. Remove the cartouche, then bake another 30 minutes until the top and edges are deep golden and crispy.
Rest for 10 minutes on the counter. Flip onto a plate and lift the pan to reveal your beautiful Pommes Anna.
