Insert a date value as a Custom Column in Power Query

So my latest challenge...

I'm in QueryEditor manipulating my data and I have a date column called 'Period'.
I want to insert a custom column which holds just the year attribute of the date cell so like =year() but i'm not sure how to include this in the Custom column formula box.
I've tried =year[Period] but that errors.

It's ok I figured it out - duplicate the Period column, the change to Year in the Date dropdown!