Put the flour and butter in a large bowl, then use your fingertips to pinch the cubes of butter in the flour. Keep doing this until the mixture resembles a breadcrumb consistency.
Next, add the sugar and the water, then use a wooden spoon or a spatula to stir the mixture until it starts binding.
Pour the rough dough out onto a flat surface, then use your hands to firmly push the pastry together until you get a nice smooth, sweet pastry.
Wrap the sweet pastry in cling film, then let it rest in the fridge for 20 minutes.
Lightly grease a tart tin with butter. Dust some flour over it so it sticks to the butter, Once you have coated the tart case with the flour, shake off the excess and set aside.
Gently lift the pastry by rolling it up on the rolling pin, then carefully unroll it over the tart tin. Carefully ease the pastry into the bottom edges. Use a fork to just lightly poke a few holes in the pastry. Chill in the fridge again for another 20 minutes. At this point, start pre-heating your oven at 180 degrees Celsius (350 degrees F).
Take your pastry out of the fridge. Get a sheet of baking paper, scrunch it up, soak it in water, squeeze out the excess water, open it up again then place it in your tart case over the pastry. Then fill with your baking beans or your uncooked rice to weigh the paper down.
Place in the oven and cook/blind bake for 10 minutes. Take the pastry out of the oven, remove the beans/rice and baking paper, then put the pastry back in the oven and cook for another 2-3 minutes.
Turn the heat of the oven down to 150 degrees Celsius (300 degrees F).
Put your butter in a small pot or pan and melt on low heat. Once the butter starts bubbling, simmer it for another 5 minutes until it develops a brown colour (be careful not to burn it).
Put your cooked pumpkin, brown butter, eggs, your egg yolk, ground cinnamon, ground nutmeg, cornflour, condensed milk and a pinch of salt in a food processor, then blitz until you have a smooth mixture.
Alternatively (if you don't have a food processor), you could put the browned butter and cooked pumpkin in a large bowl and mash together with a fork until the pumpkin gets a nice puree consistency. Add your eggs, egg yolk, sweetened condensed milk, cinnamon, nutmeg, cornflour and a pinch of salt then whisk together until well combined.
Put the blind-baked tart case on a baking tray.
Transfer the filling to a measuring jug, then you can easily pour it in the pastry case.
Start pouring the pumpkin filling in the pastry case. Once the pastry case is almost filled up (meaning you may not need to add all the filling). Carefully place in the oven and cook for 1 hour.