01 - Preheat the 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.
03 - Add buttermilk, vegetable oil, eggs, and vanilla extract. Beat on medium speed until well combined.
04 - Gradually mix in hot water until the batter is smooth. The batter will be thin.
05 - Divide the batter evenly between the prepared pans. Bake for 32-36 minutes, or until a toothpick inserted in the center comes out clean.
06 - Let cakes cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
07 - Place chopped chocolate in a heatproof bowl. In a small saucepan, heat heavy cream until just simmering. Pour over chocolate and let sit 2 minutes. Add butter and stir until smooth and glossy. Allow to cool until thickened but still pourable.
08 - Place one cake layer on a serving plate. Spread with half the caramel sauce and sprinkle with half the chopped pecans. Drizzle with some ganache. Top with the second cake layer.
09 - Pour ganache over the top, letting it drip down the sides. Spread evenly with a spatula if needed.
10 - Decorate with remaining caramel sauce, pecan halves, and additional ganache as desired. Chill for 30 minutes before slicing for cleaner layers.