Place all ingredients in a saucepan and stir well, ensuring the cornflour (cornstarch) has dissolved completely.
Once the mixture is mixed well, cook on a medium heat, stirring continuously, until thickened and gently bubbling.
Depending on the consistency and texture of your pumpkin purée, it may not properly mix into your milk - if this is the case you can either transfer the mixture to a food processor or blender or use a hand-held stick blender to blend until completely smooth.
Leave to cool slightly before pouring into the pastry.
For the pastry:
Preheat the oven to 180 degrees Celsius (350 degrees Fahrenheit).
Combine all ingredients in a large bowl along with about 7 tablespoons of water, until it forms a firm dough - add the water a few tablespoons at a time so that you don’t add too much!
You can keep this pastry dough in the fridge for up to a day if you like, but there is no need to chill it before using.
Place the pastry dough into a greased pie dish and use your fingers to carefully press it across the bottom and up the sides of the dish (I used a 9inch/22.5cm pie dish).
You can use a fork or your fingers to create a pretty pattern around the edge if you like.
Pour the filling into the pie crust just before putting in the oven (as otherwise the dough might 'melt').
Bake in the oven for around 40 minutes, until the pastry crust is firm to the touch and golden brown.
Leave to cool completely before cutting, ideally putting the pie in the fridge for a couple of hours, to allow the filling to set properly.
Tastes best when fresh, but keeps covered in the fridge for up to a few days.
*If you can't get hold of pumpkin purée, you can substitute it with butternut squash purée.**You can alternatively use almond flour.