Heat the oil in a large saucepan. Tip in the onion and fry for 6-8 minutes until softened and starting to colour. Now add in the pepper and garlic and fry for 2-3 minutes. Put in the mince and fry over a highish heat, breaking it up with a wooden spoon as you go until it is no longer raw looking. Stir in the chilli, cumin, paprika and fry for another minute.
Add the tomatoes, stock, tomato purèe and oregano. Bring the mixture to a gentle simmer and let it bubble gently away, uncovered, for 25 minutes until thick and saucy, stirring occasionally. Mix in the kidney beans and allow to simmer for another 5 minutes. Stir in the parsley, then season to taste with salt and pepper. Leave to stand for the flavours to develop.
Chop the potatoes into 5-6cm chunks and cook in boiling water for 12-15 minutes or until tender.
Preheat the oven to gas 6, 200℃, fan 180℃. Drain the potatoes well and return to the pan to dry out briefly over a very low heat. Remove from the heat, put in the butter and soured cream and mash until smooth and creamy. Season to taste with salt and pepper. Spoon the chilli mix into a 1.8-2 litre ovenproof dish. Spoon over the mash, scatter over the cheese and chilli flakes (the pie can be chilled now for up to a day ahead.) Place on a baking sheet and bake for 25 minutes until the topping is golden and the filling bubbly. (Or if made ahead and chilled overnight, bake as above allowing 40-45 minutes.)
Freezing instructions: After you have assembled the pie and before baking it as above, let it get cool completely, then cover tightly with cling film and foil and freeze (for up to 6 weeks).
To serve, defrost overnight in the fridge then cook as above, for about 40-45 minutes, or until hot and bubbly.
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