Prepare Pan - Preheat oven to 350°F (177°C). Boil about 8 cups water. Move rack to middle of oven. Lightly grease inside of bundt pan with butter or spray. Swirl cajeta along bottom of bundt pan.
Make Cake Batter - In the mixing bowl or a stand mixer, combine the cake mix with 1¼ cup water, oil, and 3 eggs. Beat on low speed to combine, about 30 seconds. Increase speed to high and mix for another 3 minutes. Cake batter will become thick and creamy. Gently layer over cajeta in bundt pan. Don't stir!
Make Flan Filling - In a blender, puree the sweetened condensed milk, 3 eggs, evaporated milk, cream cheese, and vanilla until smooth Gently pour the flan batter evenly over the cake batter. Again, don't stir!
Cook Chocoflan - Place roasting pan on middle rack in preheated oven. Carefully place filled bundt pan in middle and fill about half-way with boiling water to create a Bain Marie. Cook for 45 minutes without opening the oven door. Remove and let cool completely.
Serve - When cooled, place flat serving platter over bundt pan, wiggle it a bit to loosen the sides and then flip pan and platter over so that chocoflan now sits in all its splendor on the platter. Refrigerate until ready to serve.