Set the EGG for direct cooking without a convEGGtor at 350°F.
In a large bowl, mix the sugars together. In another bowl, combine the levener, kosher salt, flour and cocoa powder. Add the dry ingredients to the sugars and stir until well mixed.
Add the eggs to a medium bowl, and then add the sour cream and heavy cream. Stir until blended; fold in the cooled chocolate mixture.
Add the wet ingredients to the dry ingredients and whisk until well blended. Pour the batter into a prepared skillet.
Generously grease a 10-inch Cast Iron Skillet with butter. Spread the batter into the skillet, add to the EGG and bake for 40 minutes.
Remove the cake from heat and let cool. Invert the cake onto a serving plate and serve topped with whipped cream.