Preheat the oven to 325°. Line the bottoms of three 8-inch round cake pans with rounds of parchment paper. Spray the pans and the parchment paper with vegetable cooking spray.

In a large bowl, whisk the sugar with the flour, cocoa powder, baking powder, baking soda and salt. In a small bowl, whisk the buttermilk with the eggs and vanilla. In another small bowl, melt the butter in the hot coffee. Using an electric mixer, beat half of the buttermilk mixture into the dry ingredients at low speed. Beat in half of the coffee mixture, then scrape down the bowl. Beat in the remaining buttermilk and coffee mixtures.

Pour the batter evenly between the prepared pans and bake for 25 to 30 minutes, rotating the pans halfway through baking, until the cakes are springy to the touch. Let the cakes cool in the pans for 10 minutes, then turn the cakes out onto a rack to cool completely. Peel off the parchment paper.

Put the chocolate in a large bowl. In a small saucepan, bring the cream and corn syrup to a boil. Immediately pour over the chocolate and let stand in a warm place for 5 minutes. Gently whisk the ganache until smooth. Whisk in the butter until incorporated. Refrigerate, stirring frequently, until the ganache is thick enough to spread, about 30 minutes.

In a microwave-safe bowl, combine the sugar with the water and heat for 30 seconds. Stir to dissolve the sugar. Set a cake layer on a cake plate or cake cardboard and brush lightly with the sugar syrup. Spread about 3/4 cup of the frosting onto the cake in an even 1/4-inch layer. Repeat with the remaining cake layers, sugar syrup and frosting. Spread the remaining frosting around the sides of the cake. Let the cake stand at room temperature for at least 1 hour before slicing.