Put oven rack in the middle of the oven and preheat to 350 degrees F.
Coat a Bundt pan with a little butter, then coat the bottom with ¼ cup caramel sauce and put it in a large roasting pan. (The roasting pan will serve as a water bath during baking.)
For the cake: Add the butter and sugar to a bowl and using an electric hand mixer or stand mixer, beat until light and fluffy, then beat in the egg. Sift together the flour, baking powder, baking soda and cocoa in a medium bowl. Beat ⅓ of the flour mixture, and ½ of the buttermilk into the egg mixture. Repeat, ending with the flour mixture. Blend until well incorporated.
For the flan: In a blender, combine the evaporated milk, condensed milk, cream cheese, eggs and vanilla. Blend on high for 30 seconds.
Scoop the cake batter into the prepared Bundt pan and spread evenly. Slowly pour the flan mixture over the cake batter. Cover with foil and add about 1-inch of hot water to the roasting pan.
Carefully slide the pan into the oven, and bake for 1 hour to 1 hour and 15 minutes or until the surface of the cake is firm to the touch, or an inserted toothpick comes out clean. Baking time may vary, depending on the oven. So take a peek at the cake after 1 hour. When cake is done, remove from the water bath and cool completely to room temperature, about 1 hour.
Invert a large, rimmed serving platter over the Bundt pan, grasp tightly together, and flip over. Remove the pan and scrape any remaining sauce from the pan onto the cake.