Combine all ingredients, except the lemon juice, in a large saucepan. Bring to a boil, then reduce to and simmer, stirring often, for 40 to 50 minutes. The mixture should be thick enough so that when you run your spoon through it will not close back up. Remove from the heat and stir in the lemon juice.
Let cool to room temperature. Pack into storage containers and refrigerate for up to a month. Pumpkin butter can also be frozen for up to 6 months.