Creamy chicken, leek and blue cheese pie

Ingredients

• 2 sheets frozen shortcrust pastry, thawed
• 1 tablespoon oil
• 500 gram chicken thigh fillets, trimmed, cubed
• 60 gram butter
• 2 leeks, halved, washed, chopped
• 125 gram mushrooms, sliced
• thyme sprig, leaves chopped
• 300 millilitre carton thickened cream
• 2 tablespoon plain flour
• 45 gram creamy blue cheese, crumbled
• 1 sheet frozen puff pastry, thawed
• 1 egg, beaten