Chicken, Leek and Mustard Pie

1. Preheat your oven to 200°C (fan 180°C / Gas 6). Trim and slice the leeks into half-moons, slice the mushrooms, mince the garlic, and shred or roughly chop the cooked chicken into bite-sized pieces.

2. Melt the butter in a wide, heavy-based saucepan over a medium heat. Add the leeks and a pinch of salt and cook, stirring occasionally, for about 5 minutes until softened. Add the garlic and thyme leaves and cook for 1 minute more.

3. Add the mushrooms to the pan, increase the heat to medium-high, and cook for 4–5 minutes, stirring occasionally, until they are golden and any released moisture has evaporated.

4. Reduce the heat to medium. Sprinkle the flour over the vegetables and stir to coat. Pour in the chicken stock a little at a time, stirring constantly, then pour in the double cream and stir in the Dijon mustard. Simmer gently for 3–4 minutes until the sauce thickens to a lightly coating consistency.

5. Fold the cooked chicken through the sauce. Taste and adjust seasoning with salt and black pepper. Remove the thyme stalks. Allow the filling to cool slightly before transferring to a suitable pie dish.

6. Unroll the puff pastry and lay it over the pie dish, pressing the edges to seal and trimming away any excess. Score a small cross or two slits in the centre of the pastry to allow steam to escape. Beat the egg and brush it generously over the pastry lid.

7. Place the pie on a baking tray and bake in the preheated oven for 22–25 minutes until the pastry is deep golden and puffed. Rest for 5 minutes before serving.