Leek, mushroom, fake chicken and tarragon pie

I don't eat many pies, but suddenly had a hankering for one last weekend. I think it must be something to do with the clocks going back. I thought I'd stick to the classic combination of leek, mushroom and chicken, but as I don't eat meat, I used Quorn pieces instead. As the Quorn adds no flavour, I added a range of other things to make up for this. Though this could have made everything taste quite muddled, it was actually very good.

Recipe (enough for four hearty portions):

3 medium leeks, finely sliced
Around 8 chestnut mushrooms, quartered
2 cloves of garlic, finely chopped
1 heaped tblsp chopped tarragon leaves
300g Quorn pieces, or another vegetarian equivalent
Around 300ml double cream
1 tsp English mustard
1 tblsp pecorino cheese (or a vegetarian equivalent)
2-3 tblsp olive oil
1-2 tblsp butter
Salt and pepper to season
1 pack all butter, ready-rolled puff pastry (320g)
A little milk to glaze

To make the filling, melt around a tablespoon of butter and a little oil, and when it's warm put in the mushrooms. Cook over a high-ish heat until the mushrooms start to brown, and then add in the Quorn, garlic and tarragon. Turn the heat down a little, season with salt and pepper, and cook until the garlic is cooked through and the tarragon wilted. Once it's all done, tip it out onto a plate and allow to cool. Put the rest of the butter and oil in the same pan, and cook the leeks over a medium low heat. Add about 0.5tsp salt and leave the leeks until they are soft, giving them a stir every now and again. Once fully cooked through pour in the cream, grind in a bit of pepper, add the cheese and mustard and stir well. Take off the heat and allow the leeks to cool a bit, then mix the mushrooms and Quorn back in. If the filling is ridiculously thick, stir in a little milk to loosen it. Once the filling has completely cooled, you can assembly the pie.
Spoon the filling into a suitably deep, oven-proof dish and lay the pastry over the top. Trim the edges and make some fancy shapes with the extra pastry if you want to decorate the top. Make a small cross in the centre of the pastry to let any steam escape, and brush the top with milk. Bake at gas mark 6 until the pastry is a rich golden colour.

You should end up with a richly savoury, vegetarian pie, with a crisp topping. Serve piping hot with lots of vegetables.