In a medium bowl, combine the pumpkin puree with the sweetened condensed milk, stirring until smooth.

Coat the crockpot with butter or cooking spray, then sprinkle the spice cake mix over the bottom evenly.

Pour the pumpkin mixture over the cake mix, letting it rest without stirring.

Cover the crockpot and set to high heat for the first hour.

Reduce heat to low and cook for an additional hour.

After two hours, check the texture and cook longer if too gooey.

Let cool slightly before serving, optionally with whipped cream or caramel sauce.