01 - Preheat oven to 350°F. Grease two 9-inch round cake pans and line 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 to the dry mixture. Beat on medium speed until thoroughly incorporated.
04 - Gradually mix in hot water until batter achieves a smooth, thin consistency.
05 - Divide batter evenly between prepared pans. Bake for 32-36 minutes or until a toothpick inserted in center comes out clean.
06 - Let cakes rest in pans for 10 minutes, then invert onto wire racks to cool completely before assembling.
07 - Place chopped chocolate in a heatproof bowl. Heat heavy cream in a small saucepan until just simmering, then pour over chocolate. Let stand for 2 minutes, add butter, and stir until smooth and glossy. Cool until thickened but still pourable.
08 - Position one cake layer on a serving plate. Spread with half the caramel sauce, sprinkle with half the chopped pecans, and drizzle with some ganache.
09 - Place second cake layer on top, pressing gently to secure.
10 - Pour remaining ganache over the top, allowing it to cascade down the sides. Spread evenly with a spatula if necessary.
11 - Garnish with remaining caramel sauce, pecan halves, and additional ganache as desired. Refrigerate for 30 minutes before slicing to ensure clean layers.