Amy,
Just get Betty Crocker's Triple Fudge cake mix, follow the instructions on the box. Set aside. Then in a blender blend 1 can evaporated milk, 1 can sweetened condensed milk, 1/2 cup regular milk, 2 teaspoons vanilla, and 5 eggs. Get a store bought tub of caramel sauce or make your own recipe.
Assembling instructions:
Preheat oven to 350 degrees.
Grease a bundt cake pan.
Pour about 1/2 cup of caramel at the bottom of pan.
Pour the milk (flan) mixture slowly over the caramel.
Pour the cake batter VERY slowly over the milk mixture.
Cover tightly with aluminum foil.
Place filled bundt cake pan in another larger pan filled with 2 inches of water.
Bake for 2 hours without opening the oven. It must bake for the 2 hours or it will be raw in the middle. Let it cool for an hour or so, invert onto a cake plate and top again with caramel sauce. Enjoy!