Preheat oven to 350°F. Grease and line 8 inch x 3 inch pans with parchment. Or grease and line 2 baking sheet pans.
Sift together flour, cocoa, soda, baking poser and salt. Set aside
Make sure all your ingredients are room temperature.
In the bowl of stand mixer fitted with the paddle attachment cream butter and sugar until light and fluffy.
Add eggs and yolks two at a time and beat them in well.
Combine buttermilk, vanilla and coffee. On low speed add alternating with dry ingredients, beginning and ending with dry. Make sure not to over mix
Pour into prepared pans (1,570 g of batter in each pan). Bake in preheated oven until a cake tester comes out with clinging crumbs, about 40 minutes.
Cool in pans 10 minutes, then run a butter knife or offset spatula around the edges of the cake and then flip onto a wire rack to remove from the pan. Peal off the parchment. Flip over and cool completely.
For the best results assembling a tiered cake, refrigerate the cakes until completely cool.
For the Ganache:
Combine chocolate, corn syrup and salt in a bowl.
Heat cream to a boil and pour over chocolate. Allow to sit for 2 minutes before whisking to emulsify. Whisk in flavoring.
Keep on a folded kitchen towel until ready to assemble your cakes. You want to keep it warm but not hot or it will melt you buttercream as you assemble.
Notes
Yield: 2, baking sheet pans [half sheet pans]. OR2, 8-inch x 3 inch round pans. This recipe makes a 4 layer cake. Halve the cake recipe for a 2 layer cake, and use a third of the ganache filling. Ideally, serve at room temperature. All the components taste better!