Instructions

Peel the potatoes, then slice them thinly. Heat the cream, milk and garlic in a pan. Add the potatoes, bring to the boil, then simmer gently for about 12 minutes, or until the potatoes are tender (but not falling apart). Drain the potatoes, reserving the milk. Spread the potatoes out on a large tray to cool, then chill until needed.

Heat the oil and butter. Add the onions and cook slowly until lightly caramelised. Remove from the heat and leave to cool, then chill until needed.

Roll out the puff pastry to form a 26cm-diameter disc and another disc of 28cm in diameter. Set the larger disc aside.

Layer the cold potatoes and onions on top of the smaller pastry disc, seasoning them between each layer with salt and pepper. Aim to create a slightly domed shape and leave a 2cm border around the edge. Brush the pastry border with beaten egg, then gently lay the larger pastry disc over the filling. Press the edges firmly together to seal, then brush the top with beaten egg.

Seal the edges and carve a pattern into the top pastry disc. Glaze with beaten egg and leave to rest for 30 minutes.

Make a small hole in the centre of the domed top while you heat the oven to 200°C/180°C fan/400°F/Gas 6.

Bake the pithivier for 35-40 minutes, until the pastry is golden and crisp.