Discard the seeds. If it's not already in reasonably small pulpy chunks, cut it up into roughly bite-sized pieces. Put about half a litre of pieces (measured with gaps between the chunks) into a pan with a good knob of butter (around 70g), cinnamon, cloves (you can take them out later), half a jar of stem ginger, chopped, and 2 level tablespoons of caster sugar. Cook it over medium/high heat till soft, stirring occasionally to stop it sticking. It'll only take about half an hour.
You can stop at this stage and let it cool and let the flavour develop overnight. Taste it and re-season; you want it to taste as strong as possible so that it's not insipid when mixed with the cream.
Make a pie crust (it's rather nice with the almond pastry recipe here). Bake the pie crust very lightly (don't let it change colour. But don't panic if it does).
Mix your cooled pumpkin with: 300 ml double cream, 4 eggs, 150 ml golden syrup and a pinch of salt.
The pumpkin should be soft enough to mash easily - if not, you can give it a whirl in a food processor. Pour it into your pie crust.
Bake for 2 hours at 170 C / 340 F / between gas 3 and 4.
It will rise. Let it fall. Let it cool also. Eat it gently warm with friends and cream.