1.Preheat your oven to 350°F, 325°F if using a convection oven.
2.With Crisco grease and flour a 13 x 18 raised lip jelly roll pan and set it aside until needed.
3.In a stand mixer, with the paddle attachment, add the butter, granulated sugar and brown sugar and cream together, on medium-high speed for 5 minutes, until the mixture is light and fluffy.
4.While the butter and sugars are creaming in a medium mixing bowl sift together the flour, dark cocoa powder, baking soda and the salt and set aside.
5.After 5 minutes reduce the mixer speed to medium and add the eggs, one at a time, beating well after each addition and add in the vanilla.
6.In a small mixing bowl or a large measuring cup combine the buttermilk, sour cream and the fresh brewed coffee.
7.Reduce the mixer speed to low and slowly add in the flour mixture alternately with the buttermilk mixture, starting with the buttermilk mixture and ending with the flour mixture, mix until just combined.
8.Pour batter into the prepared jelly roll pan, level out the batter and bake the cake for 25-30 minutes or until toothpick inserted into center of the cake comes out clean.
9.After the cake is baked remove it from the oven and cool it to room temperature before frosting.
10.While the cake is baking in a double boiler, over simmering water, combine the semi-sweet chocolate chips and the heavy cream and stir until the chocolate chips have melted.
11.Remove the chocolate from the heat and stir in the corn syrup and the vanilla.
12.Now let the chocolate cool to room temperature, DO NOT skip this step it is vital that the chocolate be at room temperature or slightly cool.
13.After the chocolate has cooled in a stand mixer, with the whisk attachment, add the cool chocolate and the butter and whip them together on medium speed until the chocolate icing thickens.
14.Immediately spread the icing over the cooled sheet cake and enjoy!