Step 1

Make sour cream pastry. Process flour and butter until crumbly. Add cream and yolk, process until mixture comes together. Knead pastry on floured surface until smooth, cover; refrigerate 30 minutes.

Step 2

Meanwhile, heat oil in large saucepan, cook fennel, celery and leek until softened. Add chicken and garlic; cook, stirring, until chicken changes colour. Add flour; cook, stirring, until mixture thickens and bubbles. Gradually add combined stock and cream; stir until mixture boils and thickens. Reduce heat, simmer, uncovered, about 10 minutes or until thickened; season. Transfer to 1.5-litre (6-cup) ovenproof dish. Cool 20 minutes.

Step 3

Preheat oven to 200°C/400°F.

Step 4

Roll pastry between sheets of baking paper until large enough to cover dish. Cover dish with pastry, trim edges. Seal edges with fork; use pastry scraps to decorate pie. Brush with egg white. Bake about 45 minutes or until browned.