Method

Step 1
Make the filling. Put the potato dice into a large pan. Cover with cold water, bring to the boil over a high heat and cook for about 10 minutes, until just tender enough to take the point of a knife. Drain thoroughly.

Step 2
Heat the oil in a large, heavy-based, deep frying pan. Add the onions and cook over a low heat for about 12 minutes, until very soft. Increase the heat slightly and cook, stirring, until the onions are golden brown.

Step 3
Add the mustard, cumin and onion seeds and stir fry for a couple of minutes until they start to ‘pop’. Stir in the garlic and ginger followed by the cumin powder, curry powder, garam masala, chilli powder, coriander, turmeric, salt and a few grinds of black pepper.

Step 4
Coarsely grate the tomatoes into the pan and stir well. Cook over a medium–low heat, stirring frequently, until the mixture is very thick. Season to taste, then stir in the potatoes, simmer for 1 minute, then remove from the heat and leave to cool.

Step 5
Make the pastry. Put both flours, the turmeric and a few grinds of black pepper into a large, heatproof bowl. Rub in the butter until the mixture resembles fine crumbs.

Step 6
Make a well in the centre. Melt the vegetable fat with the salt and 200ml of water in a medium pan over a low heat. Bring the mixture to the boil, then tip it into the well.

Step 7
Mix everything together with a wooden spoon, then as soon as the mixture has cooled enough to handle, turn it out onto a lightly flour-dusted worktop.

Step 8
Knead the dough for about 5 minutes, until very smooth and pliable. Cut off one quarter to make the lid, wrap it in cling film and set aside.

Step 9
To form the pastry pie case, roll out the remaining dough to a disc about 1cm thick. Set the disc on top of the cling-film-covered cake-tin base.

Step 10
Gently but firmly mould the pastry across the base and down the sides until the sides are 9cm high, with no pleats, and about 3mm thick. Chill for about 1 hour, until firm.

Step 11
Roll out the reserved pastry to a disc slightly larger than the top of the tin, cover with cling film and set aside. Re-roll any trimmings to 3mm thick and stamp out 6 shapes, for decoration, if you wish. Heat the oven to 200°C/180°C fan/400°F/Gas 6.

Step 12
Set pie case upright on the lined baking sheet, lift out the cake tin, then peel away the cling film. Spoon the filling into the pastry case and trim the sides so they are slightly higher than the filling. Brush the rim with beaten egg and top with the lid.

Step 13
Trim the lid to fit. Pinch together the edges to seal, then crimp with a fork. Brush all over with beaten egg, then attach any pastry shapes and glaze these too. Cut a couple of small steam holes in the top of the pie.

Step 14
Bake the pie for about 55–60 minutes, until golden and crisp. Remove from the oven and leave to cool.

Step 15
Make the mango chilli topping. Put the sugar and 2 tablespoons of water into a medium pan over a low heat. Warm gently to dissolve the sugar. Add the chilli slices, to taste, then simmer for 3–4 minutes.

Step 16
Cut 2 slabs of mango flesh from either side of the stone (or 4 if you have 2 mangoes). Slice thinly and add to the pan. Simmer for 1 minute, then remove with a slotted spoon. Set aside to cool.

Step 17
Finely dice the remaining mango flesh and it add to the pan. Simmer for 1 minute, then remove as before and set aside on a separate plate. Remove the chilli and leave to cool. Discard the syrup.

Step 18
Decorate the top of the baked pie with the mango slices, filling in the gaps with the diced mango. Finish with the chilli slices and sprinkle with black onion seeds.