Make the cake layers: Heat oven to 350°F (175°C). Grease and line two 8-inch pans.
Whisk dry ingredients in a bowl. In another bowl, mix eggs, buttermilk, oil, and vanilla. Add dry ingredients, then stream in hot coffee.
Batter will be thin. Divide into pans and bake 28–32 minutes. Cool completely.
Make ganache: Heat cream until steaming.
Pour over chopped chocolate with a pinch of salt. Let sit 2 minutes, then whisk smooth. Cool until spreadable.
For a whipped finish, chill briefly and whisk until fluffy.
Fill and crumb coat: Level cakes if needed. Add a thin layer of ganache and optional jam or chopped nuts between layers. Apply a thin outer coat to catch crumbs.
Chill 20 minutes.
Final coat: Add a thicker layer of ganache and smooth with an offset spatula or bench scraper. Now decorate using one of the easy design ideas below.