01 - Preheat oven to 350°F. Grease two 9-inch round cake pans and line with parchment paper.
02 - Whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large bowl.
03 - Add buttermilk, vegetable oil, eggs, and vanilla. Beat on medium speed until thoroughly combined.
04 - Gradually mix in hot water until batter achieves smooth consistency. The batter will appear thin.
05 - Divide batter evenly between prepared pans. Bake 32-36 minutes until toothpick inserted in center exits clean.
06 - Let cakes rest in pans 10 minutes. Remove and transfer to wire racks to cool entirely before assembly.
07 - Place chopped chocolate in heatproof bowl. Heat cream in saucepan until simmering. Pour over chocolate, wait 2 minutes. Add butter and stir until smooth and glossy. Cool until thickened yet pourable.
08 - Position one cake layer on serving plate. Spread half the caramel sauce evenly. Sprinkle half the chopped pecans over caramel. Drizzle with portion of ganache.
09 - Place remaining cake layer atop first tier.
10 - Pour remaining ganache over top, allowing excess to cascade down sides. Spread uniformly with spatula as needed.
11 - Decorate with remaining caramel, pecan halves, and additional ganache drizzle. Refrigerate 30 minutes before slicing for clean presentation.