Preheat your oven to 200°C (400°F).

In a large skillet, heat 2 tablespoons of olive oil and 50 grams of butter over medium heat. Add sliced leeks and sauté for 5-7 minutes until soft and translucent.

Add diced chicken breast into the pan with leeks and cook for 5-7 minutes until lightly browned.

Sprinkle 2 tablespoons of all-purpose flour over the mixture, stir thoroughly, and cook for 2 minutes.

Gradually pour in 300 ml of chicken stock while stirring to avoid lumps, and simmer for 5 minutes until thick.

Stir in 200 ml of cream and 1 teaspoon of dried thyme, season with salt and pepper to taste. Remove from heat and let it cool.

Roll out 250 grams of puff pastry on a floured surface until large enough to cover the pie dish.

Place the pastry over the filling in the pie dish, trimming excess. Press down edges to seal and cut slits for steam.

Brush the top with the beaten egg for a golden finish.

Bake for 25-30 minutes until the pastry is puffed and golden brown.

Let the pie cool for a few minutes, then garnish with fresh parsley before serving.