Preheat oven to 200 C / 180 C fan / Gas 6. Lightly grease a 23cm deep pie dish with a little butter.
Sift the flour and 1/2 teaspoon of salt into a large bowl. Rub in the butter until the mixture resembles fine breadcrumbs. Add in the water 1 tablespoon at a time until the mixture comes together to a soft dough.
Roll out the pastry onto a lightly floured surface until it is 3mm thick. Carefully lift the pastry into the prepared dish. Press gently into the sides then cut off the excess with a sharp knife. Place in the freezer for 15 minutes.
Remove the pastry from the freezer and carefully line the inside with aluminium foil and pour in some weighted beads. Bake in the oven for 20 minutes. Carefully remove the beads and foil and bake for another 15 minutes until the pastry is a light gold colour, then allow to cool.
Slice the pumpkin in half and scoop out all the seeds and stringy bits and discard. Cut the pumpkin into 8 pieces and place on a baking tray skin side up. Add 1cm of water to the tray and bake in the oven for 30 minutes.
Remove the pumpkin from the oven when cooked and leave to rest for 5 minutes. Using a spoon peel off the skin and discard. Cut the soft pumpkin flesh into smaller pieces and place in a large pan, then using a potato masher mash into a soft pulp.
Gather the pumpkin flesh into a cheesecloth and squeeze out the juices. Discard the juice, then measure the dry pumpkin pulp to 500g.
Warm the evaporated milk in a small milk pan until just above lukewarm. Lightly whisk in the eggs, sugar, spices and salt. Add the pumpkin pulp and stir.
Pour in the pumpkin mix into the pastry case. Carefully transfer to the oven and bake for 40 minutes, until the filling is set.
Pre-baking the pastry is important when dealing with wet ingredients as a filling as this reduces the chances of getting a soggy bottom. Warming the evaporated milk will help with binding the pumpkin custard before it's poured into the pastry and will further reduce chances of getting a soggy bottom.
Certain types of pumpkins are only really grown for carving with rather than cooking and may result in a stringy and lumpy pumpkin custard no matter how well you mash it. You can avoid your custard getting too stringy by passing it through a sieve before straining it in cheesecloth, and you can even further prevent it from being stringy by putting it in a food processor after straining.