Apart from the fine slicing of the spuds, this dish is a breeze to prepare, and if you've got a fancy magimix with a potato slicer attachment, it will be the work of seconds.
Preheat the oven to 200 C (180 C Fan)
9 oz/ 225 g unsalted butter
2lbs/ 900 g potatoes
Salt and pepper
Finely slice the potatoes with a sharp knife or mandoline, or push them through a magimix with the slice blade attachment in. Pop the sliced potatoes in a big bowl of cold water to wash the starch off, or rinse them thoroughly under cold, running water in a collander. Scatter then drained potato slices on to a clean tea towel and dry off most of the excess moisture.
Melt the butter in a small saucepan and, using a pastry brush, paint the inside of your gratin dish with melted butter. I made them this time in mini cast-iron lidded pots, but if you don't have any, use a larger, shallow cast-iron pan or an oven-proof dish will do just fine. Line your dish with potato slices in overlapping concentric circles, brush with more melted butter and season. Continue to layer up the potatoes in this way. Place a lid or sheet of greaseproof paper on top and bake the Pommes Anna in the oven for 45 minutes to one hour. Test the potatoes are cooked through with a skewer and take the lid/ greaseproof off for the last 15 minutes of cooking time to get a nice, brown top.
If you've used a large, shallow cast iron pan, you can upturn the potatoes on to a warm plate and, fingers crossed, the Pommes Anna will come out as a neat, whole cake, which you can slice up and serve.