Preheat oven to 350°F (175°C) and grease two 9-inch round cake pans with butter and cocoa powder.
In a large bowl, whisk together flour, sugar, cocoa, baking soda, baking powder, and salt.
Add buttermilk, oil, eggs, and vanilla to the dry ingredients and mix on medium speed until well combined.
Reduce speed and carefully pour in the hot coffee, stirring by hand until the batter is smooth and thin.
Divide the batter evenly between the two pans and bake for 30 to 35 minutes or until a skewer inserted in the center comes out clean.
Cool the cakes in the pans for 10 minutes, then transfer to wire racks to cool completely.
Heat 1 cup of heavy cream until simmering, then pour over chocolate chips; let stand for 5 minutes before whisking into a smooth ganache.
Place the first cake layer on a serving plate, spread a thin layer of ganache, followed by 1/2 cup of caramel and 3/4 cup of pecans.
Place the second cake layer on top and frost the entire cake with the remaining chocolate ganache.
Drizzle the top with the remaining caramel sauce and sprinkle with the remaining toasted pecans before serving.