Step 1: Preheat the oven

• Preheat your oven to 200°C (400°F).
• Grease your pie dish with a little butter to prevent the pastry from sticking.

Step 2: Sauté the leeks

• In a frying pan, melt the butter over medium heat.
• Add the sliced leeks and cook gently for 8-10 minutes, stirring occasionally, until softened but not browned.
• Remove from the heat and set aside.

Step 3: Make the creamy sauce

• In a saucepan, melt the remaining butter over medium heat.
• Stir in the flour and cook for 1-2 minutes to form a roux.
• Gradually whisk in the chicken or turkey stock, stirring constantly to avoid lumps.
• Cook for 3-4 minutes until the sauce thickens, then stir in the double cream, Dijon mustard, and fresh thyme (if using).
• Season with salt and pepper to taste, then remove from the heat.

Step 4: Combine the filling

• Add the cooked turkey and sautéed leeks to the sauce, stirring gently to combine.
• Taste and adjust seasoning if needed.
• Pour the filling into the prepared pie dish.

Step 5: Add the pastry topping

• Roll out the shortcrust pastry on a floured surface, large enough to cover the pie dish.
• Drape the pastry over the filling and trim any excess around the edges.
• Press the edges of the pastry to seal, then cut a small slit in the center to allow steam to escape.
• Brush the pastry with beaten egg for a golden, shiny finish.

Step 6: Bake the pie

• Place the pie in the preheated oven and bake for 25-30 minutes, or until the pastry is golden brown and crisp.
• Once baked, remove from the oven and let the pie rest for a few minutes before serving.