Place the semisweet chocolate, espresso powder and salt in a bowl. Heat the heavy cream until steaming, pour it over the chocolate and let it stand for 3 minutes before stirring until smooth. Refrigerate for 2 to 3 hours, until thick but not solid.
Heat the oven to 350 F. Grease and line two 8-inch round cake pans, then whisk together the flour, sugar, cocoa powder, espresso powder, baking soda, baking powder and salt.
Whisk the eggs, buttermilk, oil and vanilla in a separate bowl. Add the wet ingredients to the dry ingredients, then gradually whisk in the hot coffee until smooth. The batter will be thin.
Divide the batter between the pans and bake for 28 to 33 minutes, until the centers spring back and a tester has a few moist crumbs. Cool in the pans for 15 minutes, then turn out and cool completely.
Beat the chilled ganache on medium speed just until it becomes lighter in color and holds firm, spreadable peaks. Stop beating as soon as it is fluffy to prevent a grainy texture.
Spread whipped ganache over one cake layer, add the second layer and cover the top and sides with the remaining ganache.
Finish the cake with shaved dark chocolate and a light dusting of cocoa powder. Let it stand at room temperature for 20 minutes before serving.