Heat 2 tablespoons of oil in a large frying pan over medium heat. Add the sliced leeks and sauté for about 5 minutes until they soften and become translucent.

Add cubed chicken thighs, browning them for around 5–7 minutes until they are no longer pink.

In the same pan, reduce heat slightly and melt 50g of butter. Stir in 50g of plain flour to create a roux, cooking for 1-2 minutes until it’s a light golden color.

Gradually whisk in 600ml of chicken stock until thickened (about 3-4 minutes). Mix in 150ml of double cream and a handful of chopped tarragon, and season with salt and pepper.

Pour the filling into a 1.2-liter pie dish, smoothing the top with a spatula.

Preheat oven to 200°C (fan 180°C/gas 6). Lay the puff pastry over the filling, sealing the edges and cutting a steam vent.

Brush the pastry with beaten egg and bake for 25-30 minutes, until golden brown.