Preheat the oven to Circotherm® 200C and line two baking trays with baking parchment.
Unroll one of the rolls of pastry and sprinkle on the plain flour. Place the second roll of pastry on top of the first (the flour will stop the pastry sticking together).
With a sharp knife, cut out 6 pumpkin shapes (basically a squashed circle with a stalk sticking out of the top). If you have lots of leftover pastry, you can re-roll and re-use – just remember to have two layers of pastry when you cut. You can use a pumpkin shaped pastry cutter if you prefer.
Separate the two layers of pastry, and place the bottom layers on the prepared baking trays. Keep them matching pastry tops in order so you remember which tops go with which bottoms (not necessary if you’ve used a pastry cutter as the shapes will be uniform).
Cut little faces out of the pastry tops. Cut small triangles for the eyes and a jagged smile for the mouth. A half-moon smile with one-tooth also looks good. Tip: It’s easier to cut if your pastry is cold.
Place the blueberries in a small pan. Squash them slightly and heat on a medium heat for 4-5 minutes, stirring and squashing regularly, until the blueberries release their liquid. Mix the corn flour with a splash of cold water and stir, then stir into the blueberry mixture to thicken the sauce. Leave to cool for a few minutes whilst you make the pumpkin filling.
In a bowl mix together the pumpkin puree, one of the eggs, the light brown sugar, cinnamon, ginger, allspice, vanilla and salt.
Spoon the pumpkin mixture into the middle of the pastry shapes that are on the trays and spread out, leaving a 1cm border.
Whisk the remaining egg and brush the 1cm border with the egg wash.
Spoon the blueberry mixture on top of the pumpkin and place the pastry tops on top. Use a fork to crimp all the way around the edges.
Brush the tops with more egg wash and sprinkle on the demerara sugar.
Place in the oven for 15 minutes until the pastry is golden and blueberry sauce is leaking slightly from the eyes and mouth (for an extra ghoulish look!).