Preheat the oven to 350°F. Line 2/ 8" pans with parchment paper. Grease the pans with butter and dust with cocoa powder.
Combine all the dry ingredients in the bowl of the stand mixer. Set the mixer with the paddle attachment. Mix all the dry ingredients until well combined.
In a separate bowl, combine the eggs, oil, milk, sour cream, and vanilla, Whisk until all ingredients are combined,
Slowly pour the wet ingredients into the dry ingredients, mix until they are fully incorporated.
Add the melted chocolate, and mix on low speed.
With the mixer on low speed, slowly start adding the hot water. Continue to mix until all ingredients are fully incorporated. The batter will be loose.
Pour the batter into the prepared pans.