Step 1

Preheat the oven to 200c/400f.

Step 2

Line a 10 x 8 inch pie dish with one roll of the puff pastry.

Step 3

Prick the base several times with a fork and cut off any large overhanging bits of pastry.

Step 4

Line the pastry with baking parchment so that it completely covers the pastry, then fill with baking beans (or dried beans) and place in the oven to 'blind bake' for 10 minutes. PRO TIP This helps to prevent the pie having a soggy bottom. Because it's puff pastry the sides will puff up a bit (which I don't mind), if you want to prevent this, just fill up with more baking beans.

Step 5

Take out of the oven and put to one side.

Step 6

Meanwhile, place the chicken, carrots, potatoes, salt, pepper, thyme and stock to a large saucepan.

Step 7

Bring to the boil and allow to simmer for 15 minutes and then turn off the heat.

Step 8

When the chicken and stock is nearly cooked, take another large sauce pan and add in the butter and chopped onion. Heat on medium and cook the onion for about 5-6 minutes until soft.

Step 9

Add in the flour and mix it into the onions and butter using a balloon whisk. It should form into a creamy paste (or roux). Allow the roux to cook for a minute whilst stirring with your whisk.

Step 10

Then add in a ladle of the stock from the chicken broth (try to get mostly stock - not the chicken/veggies). Stir the broth into the mixture using the whisk. Repeat this until you have ladled out most of the stock from the chicken pan (leaving the chicken and veggies behind).

Step 11

Now pour in the milk. Heat through whilst stirring with the whisk. The sauce should thicken as it is heating.

Step 12

Once the sauce is almost at boiling (don't let it boil) add in the chicken and veggies.

Step 13

Bring back to almost boiling and add in half the lemon juice. Give it a stir and taste. Add the rest of the lemon juice and a more seasoning if you think it needs it.

Step 14

Remove the baking beans and baking parchment from the pie and fill the pie up with the chicken mixture.

Step 15

Brush the edges of the pastry with egg wash, then top the pie with the remaining piece of pastry.

Step 16

Pinch the edges to seal, then brush the top with more egg wash and pierce a couple of small holes in the top of the pie with a sharp knife.

Step 17

Place back in the oven (still at 200c/400f) and cook for 20-25 minutes until golden brown.

Step 18

Serve immediately with some green veg.