Take a look at the Supported format specifiers for DATETIME_FORMAT.
It seems that you want the month number followed by the month name, with a hyphen in between.
With the DATETIME_FORMAT function, ‘MM’ will display the number of the month (with a preceding zero if necessary), and ‘MMMM’ will display the month name.
So, if your date field is “Date Field”, then use the formula:
DATETIME_FORMAT({Date Field},‘MM-MMMM’)
(Edited post to change “M” to “MM”.)