Start of with a base colour (either white or blue or any colour preference you want), fill the cookie with white or blue flood icing. Let it dry for a few hours.
Then the first step is pipe a line from one end of the snowflake tips to the other end using a stiff consistency icing - see picture below.
Then continue to do the swirls on each snowflake tips and put a tiny dot on each side - as pictured below
It doesn't show well in photos but it sure looks pretty when you see it up close ;-)
and be merry! :)