Power Query - date from month and year

Apologies if this is a duplicated post but, each time I post it, I see no evidence that it's been added to the forum.

I have a date field "DD-MM-YY" from which I need to create a date "1-MM-YY" i.e. I'm not interested in the day, just the month and year. 

So far I have managed to extract the month and year from the original date:

= Table.AddColumn(#"Added No. of breaches", "Breach_Month", each Date.Month([Breach_date]))

= Table.AddColumn(#"Added Custom", "Breach_Year", each Date.Year([Breach_date]))

but how do I now create the date "1-Breach_Month-Breach_Year"?

I want to do this in Power Query, not in Dax.