To make the pastry, sift the flour, cumin and turmeric into a bowl. Using your fingertips, rub in the butter until the mixture resembles fine breadcrumbs. Make a well in the centre and add the egg yolks and the chilled water. Mix with a flat-bladed knife, using a cutting action, until the mixture comes together in beads. Lift onto a lightly floured work surface and gently gather into a ball. Cover with plastic wrap and refrigerate for 30 minutes.
Lightly grease two deep 12–hole patty pans or mini muffin tins. Roll out two-thirds of the pastry to about 2mm (1/16inch) thick, and cut 8cm (3¾inch) rounds to fit the tins. Place the pastry in the holes. Roll out the remaining pastry and cut 24 tops with a 5.5cm (2¼inch) cutter. Chill the pastry.
To make the filling, heat the butter in a large saucepan and cook the onion until soft. Add the chicken and, when browned, stir in the curry powder and cumin seeds for 2 minutes. Add the flour and stir for 30 seconds. Remove from the heat and gradually stir in the stock. Return to the heat and stir until the sauce boils and thickens. Reduce the heat and simmer for 2–3 minutes, or until reduced and very thick. Stir in the mango chutney and coriander. Season and cool.
Preheat the oven to 180°C (350°F/Gas 4). Divide the filling equally among the pastry cases and brush the edges with water. Lay the pastry tops over the pies and press around the edges with the tip of a sharp knife. Slash each top to allow steam to escape. Brush with milk and bake for 30 minutes. Cool slightly before removing from the tins. Serve warm.