Combine all ingredients in a slow cooker and mix well.
Cover and cook on high for 3 hours- stirring occasionally to prevent scorching.
To Can* (see note below): Fill jars 3/4 of the way full and secure canning lids. Place jars in a pot with a shallow boiling water bath for 40 minutes (or 20 minutes in a pressure canner with 10 lbs of pressure)
*Note: While the original recipe for pumpkin butter provided a canning method, it is no longer recommended: https://foodinjars.com/2010/10/canning-101-why-pumpkin-butter-cant-be-canned/