With a sharp knife peel the squash, then remove the seeds with a spoon and chop the flesh into small cubes. Transfer the cubes into a large pot and add the sugar.
Mix well and cover the pot with the lid, then let it rest for at least 6 hours or overnight.
After the resting time, the pumpkin will have released all its liquids; add the pumpkin spices and the lemon juice, then turn on the heat to low and cook for at least 1 hour.
When the pumpkin is soft, mash it with a fork or with an immersion blender. You can decide the actual consistency of the jam, if you prefer it more chunky or not.
With a spoon, or with the help of a funnel, pour the jam into the sterilized jars (see post for details) leaving ½ cm on top and close them well. Turn the jars upside down until completely cooled.
For the Chestnut Cookies
Add the flour, cold butter and salt in a blender and blend until you will have a crumbly sand-like dough.
In a bowl mix the sugar, egg yolks and hazelnut crumbs, then add the crumbly mix and with your hands combine all the ingredients until you have a smooth ball of dough. Cover in foil and let it rest for about 20 minutes in the fridge.
Pre-heat the oven at 180°C (350°F), then dust with flour a wooden board and roll the dough into a sheet about ½ cm (0.20 in) thick.
Cut the cookies in whichever shape you prefer and place them in a baking sheet covered with parchment paper.
Bake for 10-12 minutes or until lightly golden.
Notes
Try to make a cookie sandwich with this pumpkin jam in the middle. So delicious!