My husband's favourite hearty steak pie!

This recipe is taken from Jamie Oliver's book "Jamie at home". It's a very nice and delicious meal full of different flavours. Ideal for a warm winter dinner, but can be cooked any season you wish, I guess :) My husband absolutely loves this one!
The downside of cooking a pie like this one is that it takes a long time, so best to cook the meat in one night and bake a pie on the next day. 
It tastes amazing!

Ingredients:
3 medium red onions, peeled and chopped
3 cloves of garlic, peeled and chopped
30g butter, plus extra for greasing
2 carrots, peeled and chopped
2 sticks of celery, trimmed and chopped
4 field mushrooms, peeled and sliced
1kg brisket of beef or stewing beef, cut into 2cm cubes
A few sprigs of fresh rosemary, leaves picked and chopped
1 x 440ml can of Guinness (no lager, please!)
2 heaped tablespoons plain flour
200g freshly grated Cheddar cheese
500g best-quality ready-made all-butter puff pastry
1 large free-range or organic egg, beaten
Olive oil
Sea salt and freshly ground black pepper

Method:
In a large saucepan, heat a glug of olive oil on a low heat. Add the onions and fry gently for about 10 minutes – try not to colour them too much. Turn the heat up, add the garlic, butter, carrots and celery and scatter in the mushrooms. Mix everything together before stirring in the beef, rosemary, a pinch of salt and a level teaspoon of pepper.
Fry fast for 3 or 4 minutes, then pour in the Guinness, stir in the flour and add just enough water to cover. Bring to a simmer, cover the pan with a lid and leave to simmer on the stove for about 2½ hours. Give the stew a good stir time to time, make sure it won't burn to the bottom of the pan. Cook until the meat is very tender and the stew is rich, dark and thick. If the stew is to liquidy just take the lead off and cook for a bit longer until the sauce thickens. Remove from the heat and stir in half the cheese, then season carefully and leave to cool slightly.
Cut about a third of the pastry off the block. Dust a clean work surface with flour and roll both pieces of pastry out evenly with a floured rolling pin to the thickness of a pound coin. Butter a deep pie dish, then line with the larger sheet, leaving the edges dangling over the side. Tip the stew into your lined dish and even it out before sprinkling over the remaining cheese. Brush the edges of the pastry with a little beaten egg.
Cut the other rolled sheet of pastry to fit the top of the pie dish and criss-cross it lightly with a sharp knife. Place it over the top of the pie and fold the overhanging pastry on to the pastry lid to make it look nice and rustic. Brush the top with beaten egg, then bake the pie directly on the bottom of the oven for 45 minutes, until the pastry is cooked, puffed and golden. Delicious served simply with peas or mash vegetables.

Tip:
Instead of a big pie you can also make several smaller ones, you can even freeze them for later.