In a medium bowl, combine the pumpkin puree and sweetened condensed milk, stirring until the mixture is smooth and creamy.

Generously grease the inside of your crockpot to prevent sticking. Sprinkle the spice cake mix evenly at the bottom.

Gently pour the pumpkin mixture over the cake mix in the crockpot, avoiding stirring to maintain distinct layers.

Cover the crockpot and cook on high for 1 hour, then switch to low and continue to cook for an additional hour.

After two hours, remove the lid and gently mix the cake with a spatula to blend the layers into a uniform batter.

Cover again and continue cooking on low for an additional 1 to 2 hours, checking for doneness with a toothpick.

Allow the cake to cool for at least 15 minutes before carefully removing it from the crockpot.