Preheat the oven to 180°C.
Cut the pumpkin in half, scoop out the seeds and peel. Cut the pumpkin flesh into small cubes.
Heat a saucepan to hot and add a knob of butter. Add the pumpkin to the pan, cover with a lid and cook for 20 minutes, stirring occasionally. Once cooked, mash the pumpkin to a smooth puree.
Line your tart case with the pastry and prick the base with a fork. Line the pastry case with baking parchment, add baking beans and blind bake for 15 minutes.
Add the brown sugar, spices and the creme fraiche to the pumpkin. Beat together the eggs and the milk and then mix into the pumpkin.
Pour the puréed pumpkin into the tart case, transfer to the oven and cook for 45 minutes. The tart should wobble slightly in the centre. Set aside and allow to cool.
For the chantilly cream: mix together the cream and the sugar and whisk until thick. Keep in the fridge until ready to serve alongside the pumpkin tart.