Heat the oil in a saucepan, add the mince and onion and fry, stirring, until the mince is browned. Stir in the garlic, chillies, cinnamon, sugar and bay leaf. Mix in the tomatoes, kidney beans and stock, then add plenty of salt and pepper. Bring to the boil, stirring, then cover and simmer gently for 45 minutes. Leave to cool.
Make the pastry. Add the flour, polenta, fats and a little salt and pepper to a bowl. Rub in the fats with your fingertips or an electric mixer until you have fine crumbs. Add enough water to form a smooth dough, then knead lightly on a surface dusted with flour.
Cut the pastry in half, roll out one half and trim to a 12 × 38 cm (5 × 15 inch) rectangle, then cut into 3 × 12 cm (5 inch) squares. Spoon half the filling into the centre of the pastry squares. Brush the edges with beaten egg, then bring the points of the pastry up to the centre, pressing the straight edges of the pastry together.
Transfer to an oiled baking sheet and repeat with the remaining pastry and filling to make 6 pies. Brush the pies with beaten egg, then bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 20 minutes.
Serve hot with soured cream and chunky salsa.