Chicken & tarragon pie with polenta crust

Make polenta pastry. Process sifted flour, polenta and butter until mixture resembles breadcrumbs. Combine egg and the water; reserve 1 tablespoon for brushing. Add remaining egg mixture to flour mixture, process until pastry begins to come together. Turn onto a work surface; knead lightly into a ball. Wrap in plastic wrap; refrigerate 2 hours.

Meanwhile, heat half the oil in a large frying pan over medium heat; cook chicken, in batches, until browned. Drain on paper towel. Heat remaining oil in same pan; cook leek and kumara, stirring, 3 minutes. Add wine and stock; cook, stirring occasionally, for 10 minutes, or until most of the liquid has evaporated. Remove from heat; stir in chicken, combined crème fraîche and flour, then tarragon. Cool.

Cut pastry in half. Roll out one half on a floured work surface until large enough to line a deep 23cm (9¼-inch) springform pan or deep pie tin. Ease pastry into pan; press into base and side. Cover; refrigerate 1 hour.

Preheat oven to 200°C/400°F; heat an oven tray.

Spoon chicken mixture into pastry case; brush pastry edge with a little of the reserved egg mixture. Roll out remaining pastry on a floured work surface until large enough to cover filling. Lift pastry onto filling; press pastry together to join. Trim edge, then press to seal with a fork. Brush top of pie with remaining reserved egg mixture; sprinkle with polenta.

Place pie on hot tray; bake 20 minutes. Reduce oven to 180°C/350°F; bake a further 25 minutes or until pastry is golden. Stand pie in pan for 10 minutes before serving.