Steps

1. Preheat oven to 350°F. Butter two 9-inch cake pans and line their bottoms with parchment paper.
2. In a bowl, sift together the flour, salt, baking soda and baking power. In another bowl, combine the hot coffee, cocoa powder and unsweetened chocolate. Stir to melt the chocolate and set aside to cool.
3. In the bowl of an electric mixer, beat together the butter and brown sugar until light and fluffy. Add eggs one at a time, allowing each to be incorporated before adding the next.
4. Reduce mixer speed to low and add 1/3 of the dry ingredients. Next add half the coffee-chocolate mixture. Repeat with the remaining dry and wet ingredients. Allow each addition to be incorporated before adding the next and finish with the final 1/3 of the dry ingredients.
5. Pour into the prepared cake pans and bake for 25-30 minutes or until the cakes spring back to the touch and have begun to pull away from the sides of the pan. Set aside to cool completely before frosting.
6. For the frosting, whisk together the cream, yolks, sugar, vanilla and salt in a medium saucepan. Set over medium-low heat and simmer, stirring constantly until thickened. Remove from heat and stir in the semisweet and unsweetened chocolate and the butter until melted completely. Finally, stir in the corn syrup and sour cream till smooth and allow to cool completely before the frosting cake.

Notes

There are moments in life when nothing will do except a slice of chocolate cake. The shiny fudge frosting stands up well to all the richness of the Devil's food cake. It's satiny and it spreads beautifully.