For caramel sauce, heat sugar until dissolved and golden. Add
butter in small pieces. Add cream in steady stream. Pour caramel
in pan, let cool.
For flan, mix all ingredients in a mixer.
For cake, follow cake box instructions to make cake batter.
Pour batter into a pan, then add flan mixture slowly on top. Put pan
(or 2 pans) in larger pan with boiling water.
Bake 50-60 minutes.
Refrigerate up to 3 days.