For the spiced pumpkin purée, bring a small amount of water to a simmer in a pan. Suspend a steaming basket above the water (do not allow the base of the basket to touch the water). Add the chopped pumpkin and steam for 15-20 minutes, or until tender. Remove from the steaming basket and set aside to cool.
When the pumpkin has cooled, transfer it to the bowl of a food processor. Add the orange juice, allspice and honey and blend until smooth and well combined.
For the cocktail, pour the bourbon, sour cherry liqueur, herb liqueur and pumpkin purée into a cocktail shaker. Add ice and shake well.
To serve, strain the mixture into a flute glass. Garnish the surface of the cocktail with a few toasted pumpkin seeds. Dust with a little freshly grated nutmeg.