Which is correct? `Once for all’ or `once and for all’?

The dictionaries list only `once and for all’. The expression is used to mean `now and for the last time’. When you do something once and for all, you finish doing it so that you don’t have to worry about it again.

*After she completes the project, Seetha plans to return to France once and for all.

Source: S. Upendran, The Hindu ‘Know Your English’ Series, March 27, 2006