Add the pumpkin puree, granulated sugar, brown sugar, apple juice, ground cinnamon, ground nutmeg, ground cloves, ground ginger, and ground allspice to your slow cooker.
Mix Well:
Stir all the ingredients together thoroughly to ensure they are well combined.
Cook:
Cover the slow cooker and cook the mixture on low for 5-6 hours. Stir occasionally to prevent sticking and to help the flavors meld. The mixture should become thick and darkened as it cooks.
Thicken the Butter:
For the last hour of cooking, remove the lid from the slow cooker to allow excess moisture to evaporate, helping the pumpkin butter thicken further.
Cool and Store:
Once the cooking time is complete, allow the pumpkin butter to cool completely. Transfer it to airtight containers.
