01 - Preheat the oven to 350°F. Grease a 9x13-inch baking pan and line with parchment paper to facilitate easy removal.
02 - In a large mixing bowl, whisk together granulated sugar, all-purpose flour, unsweetened cocoa powder, baking powder, baking soda, and salt until evenly distributed.
03 - Add eggs, buttermilk, vegetable oil, and vanilla extract to the dry mixture. Blend until just combined.
04 - Pour in hot coffee and stir until the batter becomes smooth and glossy; batter will appear thin.
05 - Transfer the cake batter into the prepared pan, spreading it evenly over the surface.
06 - In a separate bowl, beat softened cream cheese and unsalted butter until creamy. Add eggs one at a time, mixing thoroughly after each addition.
07 - Sift in powdered sugar and cocoa powder. Add vanilla extract and salt, then continue beating until the mixture is smooth and fluffy.
08 - Gently spread the gooey layer evenly over the cake batter.
09 - Bake for 32 to 38 minutes, or until edges are set and the center remains slightly wobbly. Avoid overbaking—the center should retain some gooeyness.
10 - Allow to cool completely before slicing. Serve at room temperature or gently warmed.