Grease a baking pan with butter, then spread dulce de leche (cajeta) on the bottom and refrigerate. Prepare the chocolate cake mix as directed on the box and pour it into the greased pan.

In a blender, blend the sweetened condensed milk, evaporated milk, cream cheese, vanilla extract, and eggs until smooth. Carefully pour this mixture over the cake batter in the pan.

Cover with aluminum foil to prevent water from getting in, and bake in a water bath for 1 hour and 15 minutes. Let cool for 1 hour, then decorate as desired.