Dauphinoise, truffle & cranberry pie

The day before serving, make the dauphinoise, caramelised onions and pastry. For the dauphinoise, preheat the oven to 190°C/170ºC fan/gas 5. In a large pan, melt the truffle butter, then take off the heat and mix in the cream, garlic, thyme, porcini paste, salt and pepper. Line a roughly 36x28cm roasting tin with baking parchment. Add a ladle of cream mixture, then a layer of overlapping potato slices, followed by another ladle of cream and a sprinkling of truffle Cheddar. Repeat 3-4 times, until all the potatoes, cream mixture and Cheddar are used up. Season the top. Cover the tin with a sheet of baking parchment and tightly cover with foil. Bake for 40 minutes, then remove the foil and parchment. Cook for another 15-20 minutes until the top is golden and the potatoes tender to the point of a knife. Leave to cool at room temperature for 10 minutes, then chill until completely cool.

Meanwhile, for the onions, heat the oil in a large pan over a medium heat. Add the onions and salt, then cook for 25-30 minutes, stirring regularly, until soft, dark brown and caramelised. Finally, stir in the truffle butter and allow to cool.

For the pastry, in a large bowl mix the flour and salt, then rub in the butter with your fingertips until you have a crumble-like texture. Tip the eggs into the flour bowl with 70ml cold water. Mix quickly until just combined, then knead gently until it’s formed a dough (add a splash more water if it’s too dry). Separate into 2 pieces, one slightly larger than the other, then cover and chill for at least 30 minutes. Once chilled, lightly flour the worktop and use a rolling pin to roll both circles to a 0.5cm thickness. Loosely cover and chill again until ready to assemble.

When ready to assemble, spray the insides of a 23cm springform cake tin with oil, then line the base and sides with the larger piece of pastry, trimming and reserving any excess. Cut a circle out of the chilled dauphinoise, slightly smaller than the base of the cake tin. Use the offcuts to form a layer of dauphinoise on the pastry base, pressing down evenly. Layer on the caramelised onions and sliced Tunworth or Camembert, then scatter over the chopped cranberries. Place the dauphinoise circle on top and press down gently. Brush the pastry edges with beaten egg, then lay the pastry lid on top, crimping the edges with a fork. Brush the top with the remaining egg. Cut a small vent in the top for air to escape. You can make a decoration with the pastry offcuts (I like to make a bow). Chill for at least 15 minutes.

When ready to bake, preheat the oven to 210°C/190ºC fan/gas 7. Bake the pie for 40 minutes until the pastry is cooked, golden and crisp. Rest for 20 minutes, then carefully transfer to a serving plate, slice and serve.