2) In a large bowl, whisk together the pumpkin, granulated sugar, brown sugar, egg yolks, orange zest, cinnamon, nutmeg and salt. Set the bowl of rum/gelatine over a pan of simmering water and heat until the gelatine is clear. Immediately whisk the hot gelatine mixture into the pumpkin mixture.
3) In the bowl of an electric mixer fitted with a whisk attachment, whip 360ml of the double cream and 1 1/2 tsp of the vanilla until soft peaks form. Fold the whipped cream into the pumpkin mixture.
4) Put the remaining double cream and vanilla in the mixer with the caster sugar and whip until soft peaks form. Reserve some of the sweetened whipped cream to serve.
5) To assemble, spoon some of the pumpkin mixture into parfait glasses, add a layer of whipped cream, then some chopped biscuits. Repeat, ending with a third layer of pumpkin. Cover with cling film and refrigerate for 4 hrs or overnight.
6) To serve, decorate with a final layer of the whipped cream. Add a ginger biscuit and slivers of crystallized ginger, if desired.