In a large saucepan, combine the pumpkin puree, sugar, and brown sugar.
Stir the mixture over medium heat until the sugars dissolve completely.
Add the cinnamon, nutmeg, cloves, and salt to the pumpkin mixture.
Stir continuously to ensure spices blend evenly.
Bring the mixture to a gentle boil, then reduce the heat to low.
Let it simmer for about 25 minutes, stirring occasionally.
Once the mixture has thickened, stir in the lemon juice and vanilla extract.
Mix well to incorporate these last ingredients.
Remove from heat and allow the pumpkin butter to cool slightly before transferring to a jar or airtight container.
This can be stored in the refrigerator.