Meat and Potato Pie

This was my Dad's absolute favourite. I always thought it was difficult to make because it is so tasty, but it is really easy.
I buy 500g of best beef that has been trimmed and diced. Mum buys a cheaper cut because she says that it is the fat and tendons breaking down that give the lovely taste. I put this in a saucepan with a large chopped onion. I then put 4/5 large teaspoons of gravy granules in and to the pot and mix these into the beef and onions. I then put about 3/4 pint of cold water in and stir continually while the mixture comes to the boil. It is then left to simmer for about 2 hours. Stir every so often and add more water if it is needed.
Set the oven to 180C/Gas Mark 4. I then peel and thinly slice 750g of potatoes. As with other recipes, I use baking potatoes because they don't go to mush. I boil these for about 10 minutes.
In a large baking dish, I spoon out the beef and use this as the bottom layer. The sliced potato is then arranged neatly over the top. You should have quite a bit of gravy. Spoon some over the potatoes and it will soak in. Keep the rest to pour over any vegetables.
I never make my own pastry. Why bother when there are so many excellent ready prepared fresh/frozen ones available? It really doesn't matter if it is puff pastry or shortcrust for this recipe. I prefer puff but hubs likes shortcrust so that is what we tend to have. And it makes less mess when you eat it!
Roll the pastry out (if you need to) so that it is just bigger than the baking dish. Place it over the top. I always crimp the shortcrust round the edge of the dish, and cut 2 small holes with a knife for the steam to come through. Decorate with left over pieces of pastry if you want to. Then cook for at least 30 minutes or until the pastry is cooked.