Step 1: Preheat your oven to 350°F (175°C). Generously grease and flour a 10-12 cup Bundt pan. Pour the caramel topping evenly into the bottom of the prepared Bundt pan.
Step 2: Prepare the chocolate cake batter according to the package directions. Pour the cake batter gently and evenly over the caramel sauce in the Bundt pan.
Step 3: In a blender, combine the evaporated milk, sweetened condensed milk, eggs, vanilla extract, and softened cream cheese (if using). Blend until completely smooth.
Step 4: Very carefully and slowly, pour the flan mixture over the cake batter in the Bundt pan.
Step 5: Place the Bundt pan inside a larger roasting pan. Carefully pour hot water into the roasting pan, around the Bundt pan, until it reaches about halfway up the sides of the Bundt pan. This creates a water bath.
Step 6: Bake for 60-90 minutes, or until a toothpick inserted into the cake layer comes out clean and the flan is set but still slightly jiggles in the center. Baking time may vary depending on your oven.
Step 7: Carefully remove both pans from the oven. Remove the Bundt pan from the water bath and let it cool on a wire rack for at least 1 hour.
Step 8: Once cooled to room temperature, cover the Bundt pan with plastic wrap and refrigerate for at least 4-6 hours, or preferably overnight. Chilling is crucial for proper setting.
Step 9: When ready to serve, run a thin knife around the edges of the cake where it meets the pan. Place your serving plate upside down over the Bundt pan, then quickly and confidently flip them over. The cake should release, with the caramel coating the flan and cake layers.