For the Cake:

1. Preheat the oven to 350 degrees. Grease 2 9-inch baking pans (see other size options below) with butter or nonstick cooking spray, line with parchment paper, and then grease the parchment paper. 
2. In a large bowl, sift together the flour, cocoa powder, baking soda, baking powder, and salt.
3. Add the sugar and whisk until combined. Set aside.
4. In another bowl, whisk together the eggs, milk, oil, and vanilla.
5. Gradually add the wet ingredients to the dry ingredients and mix until the batter is smooth.
6. Carefully add the hot coffee (or boiling water). Stir until combined. The batter will be runny.
7. Pour the batter into the prepared pans and bake until a skewer inserted into the center of the cake comes out clean, about 35-40 minutes. 
8. Let the cake cool for at least 15 minutes before removing from the pans. Let the cakes cool completely on a wire cooling rack before frosting.

For the Ganache:

1. Place the slightly cooled melted chocolate and sour cream in a large bowl and whisk to combine.  Refrigerate for 10 to 15 minutes or until firm before frosting. Sprinkle with the flaky sea salt before serving.