Beat the pumpkin with the sugar, spices, lemon juice and evaporated milk.
Whisk the cream until thick and floppy but not stiff, then fold it into the pumpkin mixture with the rum.
Freeze churn the mixture until ready to serve in an ice cream maker, adding the raisins as the mixture becomes very thick.
If you do not have an ice cream maker, freeze the ice cream in a suitable plastic container, beating it two or three times whilse freezing. An ice cream maker gives a smoother texture.