01 - Preheat oven to 350°F. Grease and line two 9-inch round cake pans with parchment paper.
02 - In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.
03 - Add buttermilk, vegetable oil, eggs, and vanilla extract. Beat on medium speed until thoroughly incorporated.
04 - Gradually mix in hot water until batter achieves smooth consistency. The batter will be thin.
05 - Divide batter evenly between prepared pans. Bake for 32-36 minutes until toothpick inserted in center comes out clean.
06 - Let cakes cool in pans for 10 minutes, then transfer to wire racks to cool completely before assembling.
07 - Place chopped chocolate in heatproof bowl. Heat heavy cream in saucepan until just simmering. Pour over chocolate and let sit 2 minutes. Add butter and stir until smooth and glossy. Cool until thickened but pourable.
08 - Place first cake layer on serving plate. Spread with half the caramel sauce, sprinkle with half the chopped pecans, and drizzle with some ganache.
09 - Top with second cake layer. Pour remaining ganache over top, allowing it to drip down sides. Spread evenly with spatula if needed.
10 - Decorate with remaining caramel sauce, pecan halves, and additional ganache drizzle. Refrigerate 30 minutes before slicing for cleaner layers.