In a medium mixing bowl, combine the canned pumpkin puree and sweetened condensed milk. Stir well until smooth and creamy.

Spray the inside of the crockpot with cooking spray. Evenly sprinkle the spice cake mix over the bottom.

Pour the pumpkin mixture over the cake mix in the crockpot, without stirring.

Cover and cook on high for 1 hour.

After 1 hour, reduce the heat to low and cook for another hour.

After two hours, gently stir and continue to cook on low for 1 to 2 hours until firm.

Insert a toothpick into the center; it should come out clean or with a few moist crumbs.

Turn off the crockpot and let the cake cool for 15 minutes before serving.