Preheat oven to 180°C/356°F.

Dice up your chicken thighs into chunks. Add some olive oil to a large pan and brown the chicken. Remove the chicken from the pan and set aside.

Finely slice your leeks, bacon and onions.

Add bacon to the chicken pan and fry until crispy. Deglaze the pan with a splash of water. Add the leeks and onion.

Fry until soft, adding a splash of water if the vegetables start catching on the pan.

Once soft, add the chicken. Stir it in and add a large handful of chopped tarragon. Stir again and flour.

Mix it in, making sure the flour is all absorbed. Pour in milk, splash by splash. Keep stirring until you have a thick pie filling. Season generously with pepper. Remove the pan from the heat.

Fill a pie dish with the filling. Lay your puff pastry on top. Trim the sides and brush the pastry with egg yolk wash. Add a sprinkle of salt and place in the oven for 30 minutes, or until the pastry is puffed up and golden.

Slice your pie up and serve with a big dollop of Dijon mustard. Enjoy!