Indian potato raised pie

Ingredients
For the filling
700g/1lb 9oz désirée potatoes, halved
2 tbsp urid dal
2 tbsp sunflower oil
1 tsp cumin seeds
2 tsp mustard seeds
10 fresh curry leaves (or 15 dried leaves)
4 red chillies, chopped
1 tsp ground turmeric
2 onions, finely chopped
salt, to taste
2.5cm/1in piece fresh root ginger, grated
2 tomatoes, finely chopped
bunch fresh coriander, roughly chopped
For the hot water crust pastry
450g/1lb plain flour
100g/3½oz strong white flour
75g/2½oz cold unsalted butter
½ tsp fine salt
100g/3½oz solid vegetable fat (such as Cookeen or Trex), plus extra for greasing
1 free-range egg yolk, beaten, to glaze

Method
Grease a 20cm/8in springform cake tin with vegetable fat.

For the filling, boil the potatoes for 15 minutes, or until tender. Drain then chop into bite-size pieces.

Soak the lentils in a cup of boiling water for 5 minutes, then drain.

Heat the oil in a frying pan. Add the cumin seeds and mustard seeds. When they splutter add the curry leaves, lentils, red chillies, turmeric and onion and mix well. Fry for 5 minutes then add the salt, ginger, potatoes, tomatoes and coriander leaves and mix well. Transfer to the fridge to cool.

Preheat the oven to 200C/400F/Gas 6.

To make the pastry, combine the flours in a large bowl. Add the butter and, using your fingertips, rub it into the flour until it resembles breadcrumbs. In a pan, heat 200ml/7fl oz water, the salt and fat until just boiling. Pour the liquid onto the flour mixture and mix using a wooden spoon.

Tip the dough out onto a lightly floured work surface and knead to a smooth dough.

Working as quickly as possible, roll out a large circle of dough and, using the rolling pin to help you, line the prepared tin.

Spoon the filling into the pastry lined tin. Press it down and level the surface.

Using the remaining pastry, roll out the pie lid on a lightly floured work surface.

Brush the top edges of the pastry in the tin with beaten egg yolk and place the pastry lid on top. Crimp the edges to seal and trim off any excess pastry. Make a couple of slits in the top of the pie to allow the steam to escape and brush the pastry lid with egg yolk. Use any leftover pastry to make decorations for the top of the pie.

Bake for 1 hour, or until the top is golden-brown. Leave to cool in the tin for 10 minutes then remove from the tins and leave to cool completely on a wire rack before serving.