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 to the dry mixture. Beat on medium speed until fully incorporated.
04 - Gradually mix in hot water until the batter reaches a smooth consistency. The batter will appear thin.
05 - Divide batter evenly between prepared pans. Bake for 32 to 36 minutes or until a toothpick inserted in the center comes out clean.
06 - Let cakes cool in pans for 10 minutes, then remove from pans and transfer to wire racks to cool completely.
07 - Place chopped chocolate in a heatproof bowl. Heat heavy cream in a small saucepan until just simmering. Pour cream over chocolate and let sit for 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.
09 - Top with the second cake layer. Pour remaining ganache over the top, allowing it to drip down the sides. Spread evenly with a spatula if needed.
10 - Decorate with remaining caramel sauce, pecan halves, and additional ganache as desired.
11 - Refrigerate for 30 minutes before slicing to ensure cleaner layers.