Prep: Preheat oven to 375°F (190°C). Grease a 10x15 inch jelly roll pan generously. Line the bottom with parchment paper and grease the paper as well.
Make Batter: In a large bowl, combine the cake mix, 6 eggs, water, and oil. Beat on medium speed for 2 minutes. The batter will be thick and glossy.
Spread: Pour batter into the prepared pan. Use an offset spatula to spread it into an even, thin layer, ensuring it reaches all corners. Tap the pan on the counter to release air bubbles.
Bake: Bake for 10–12 minutes. The cake is done when the top springs back when lightly touched. Do not overbake, or it will crack when rolling.
The Towel Roll: While the cake is baking, lay a clean kitchen towel on the counter and dust it generously with cocoa powder.
Flip & Roll: Immediately upon removing the cake from the oven, flip the hot cake onto the dusted towel. Carefully peel off the parchment paper. Starting at a short end, roll the cake and the towel up together into a tight spiral.
Cool: Place the rolled cake (still in the towel) on a wire rack and let it cool completely (about 1 hour). This sets the "memory" of the curl.
Make Filling: Whip the heavy cream, softened cream cheese, powdered sugar, and vanilla until stiff peaks form.
Fill: Gently unroll the cooled cake. Spread the filling evenly over the surface, leaving a 1-inch border. Roll the cake back up (without the towel). Place seam-side down on a platter.
Frost: Heat the 1/2 cup heavy cream until steaming. Pour over chocolate chips. Let sit 3 minutes, then whisk until smooth. Let ganache cool until it thickens to a spreadable consistency. Frost the log, using a fork to create "bark" lines.
