Mary Berry's Chicken and Bacon Lattice Pie

My sister made this for us for dinner just before we went to the Isle of Wight. It was absolutely delicious, a really homey comforting dish and definitely one I will have to try for myself.

Chicken and Bacon Lattice Pie (from BBC Food)
(Serves 6)

6 skinless chicken legs (thigh and drumstick)
4 celery sticks, diced
4 bay leaves, roughly sliced
200ml dry white wine
300ml chicken stock
250g smoked back bacon (about 7 rashers), cut into small pieces
1 large onion, roughly chopped
50g butter
60g plain flour, plus extra for dusting
2 tbsp crème fraîche
1 tbsp grainy mustard
2 x 375g packets ready-rolled, all-butter puff pastry
1 egg, beaten
salt and pepper

Preheat the oven to 160C.

Put the chicken legs, celery and bay leaves into a large ovenproof saucepan, pour over the wine and stock and season with salt and pepper. Bring to the boil over a medium-high heat, cover with a lid and transfer to the oven for 30–40 mins, or until the chicken legs are cooked and tender. Set aside to cool.

Once cool, remove the meat from the chicken bones. Break the meat into bite-sized pieces before transferring to a bowl. Strain the stock, reserving the celery and discarding the bay leaves, and measure out the liquid. You should have about 750ml; if not, make up to this amount with a little extra stock or white wine.

Heat a large frying pan and fry the bacon pieces over a medium-high heat for 3 mins. Add the onion, cover with a lid and fry for a further 10 mins until the onion is softened. Add the butter, stir until melted, and then sprinkle in the flour to make a roux. Pour the reserved liquid into the roux a little at a time, whisking as you add, and stir over a high heat until thickened to a smooth sauce consistency.

Add a little salt and pepper, the reserved celery, crème fraiche and mustard and mix to combine before adding the chicken. Spoon the filling into an ovenproof pie dish and level the top. Leave until cool and then chill, covered, in the fridge for 30 mins.

Meanwhile, prepare the pastry for the pie. On a lightly floured work surface, roll out each of the pastry sheets to about 3mm thick. Cut each piece into long, thick ribbons, about 3cm wide. You will need to make enough to cover the top of the dish, about 16 in total. Weave the ribbons together on a piece of baking paper, until you have a pastry top that is large enough to cover your pie. Chill in the fridge for 15 mins to firm up or, if time allows, freeze until solid.

Take the filling out of the fridge and brush the edges of the dish with a little beaten egg. Carefully slide the pastry lattice from the baking paper and lay on top of the chilled filling. Trim the excess pastry around the rim and lightly press to seal.

Increase the oven temperature to 200C. Brush the pastry with the remaining beaten egg and bake for 30 mins until the pastry is golden and cooked through, and the chicken is bubbling. Serve.