Add 1 tablespoon of butter to a cast iron skillet and place in the oven while mixing the rest of the ingredients together. (Does not have to be preheated.)
Combine coconut oil, 1 tablespoon of the butter, and cream cheese. Either melt on the stove or microwave.
In a separate bowl, combine flour, cocoa powder, and baking powder. Whisk until combined.
Add eggs, coconut milk, sweetener, and vanilla to the coconut oil, butter, and cream cheese mixture.
Beat on low/medium for 1 minute or until smooth.
Add flour, cocoa powder and baking powder mixture to other ingredients and beat until just combined.
Remove cast iron skillet from oven and swirl butter around so that it greases the bottom and sides of the skillet.
Pour batter in skillet and bake at 350 degrees for 15-17 minutes. Insert a knife in the middle of the cake to test doneness. Do not overbake.
Serve with homemade whipped topping and shaved unsweetened chocolate.