In a medium saucepan over low heat, combine pumpkin, brown sugar and spices. Cook for 5 to 6 minutes, or until mixture reduces by half and pumpkin looks dry. Set aside. In a medium saucepan over high heat, add cream. When cream boils, take off heat. In a heatproof medium bowl, add chocolate and hot cream. Let the mixture sit for a minute, then slowly begin to stir, starting in the center of the bowl and working outwards. Once the chocolate and cream are evenly mixed, add pumpkin mixture and whisk to combine. Add the butter and liqueur, if using. Cover tightly with plastic wrap and refrigerate until chilled.
On a parchment lined cookie sheet, scoop mixture into small balls using a melon baller. Place in refrigerator for 1 hour, or until chilled. Remove truffles from refrigerator and dip each in melted chocolate. Roll in cocoa powder and serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.