Preheat oven to 350°F. Line two or three 8-inch round cake pans with parchment paper circles and spray with baking spray or butter the cake pans and dust with cocoa powder.

In a large bowl, whisk together the flour, granulated sugar, brown sugar, cocoa powder, baking powder, baking soda, and salt.

In another bowl, whisk together the eggs, sour cream, oil, and vanilla extract. Gradually add the wet ingredients to the dry ingredients, mixing just until combined. Scrape the bottom and sides of the bowl, then mix in the hot coffee or water.

Evenly divide the batter between the prepared pans and bake for 25-30 minutes (30 to 35 minutes for just 2 cake layers) until a toothpick inserted into the center of the cakes comes out clean. Cool for 10 minutes in the pans before turning out onto wire racks to cool completely.

Make the caramel by adding the sugar to a dry, medium saucepan over medium heat. Stir constantly with a wooden spoon or heatproof spatula until melted.

Once melted, stir in the butter. The caramel will bubble up when you add in the butter, so be careful. Add the heavy cream while stirring until combined, then let the caramel boil for 1 minute without stirring.

Remove the pan from the heat and stir in the vanilla extract and salt. The caramel will be very thin at first but it will thicken as it cools. You want it pourable but thick, which is usually just slightly warm to the touch.

Make the frosting by combining the cream, corn syrup, and butter in a medium saucepan over medium-low heat. Heat just until bubbles start to appear around the edges of the pan.

Pour over the chopped chocolate and cocoa powder in a medium bowl and let sit for 5 minutes without stirring. Whisk gently until the chocolate is melted and smooth. Stir in sour cream. Let cool until thick enough to spread.

You can refrigerate the bowl for 20 minutes to speed the process up but don't leave it longer than that or the frosting will be too firm for frosting.

To assemble, place one cake layer on a cake plate and top with about ⅓ of the fudge frosting, spreading it into an even layer. Drizzle about ⅓ of the cooled caramel sauce over the fudge frosting, then sprinkle with ⅓ cup of the chopped pecans.

Repeat with the remaining cake layers, fudge frosting, pecans, and caramel, coating the outside of the cake with fudge frosting and decorating the top with whole pecans and a caramel drip, if desired.