Spray or grease the inside of the crockpot with coconut oil spray or butter.
In a medium mixing bowl, combine eggs and sweetener. Mix with a hand mixer until smooth and slightly thickened.
Add pumpkin puree and vanilla/maple extract to the egg mixture and blend.
Blend in almond flour, salt, and pumpkin pie spice. Continue to blend while slowly pouring in the melted butter/ghee/coconut oil. Pour into crockpot.
Place paper towel over top of the crockpot and cover with the lid. This will absorb any condensed moisture that forms on the lid and prevent it from dripping onto the custard.
Set to low and cook for 2-3 hours. Begin checking at the 2 hour mark. When done, the sides will pull away from the crockpot and the center will be set.
Serve warm with whipped heavy cream and nutmeg, if desired.