In a saucepan, combine the pumpkin, cider, vanilla, vinegar, syrup, sugar, salt, ginger, cardamom, and cinnamon. Simmer on medium-low for 15 to 20 minutes, until the pumpkin butter thickens and becomes spreadable. Stir occasionally. Taste and adjust seasonings. Remove from the heat and let cool. Store in an airtight container in the fridge for up to a month.