Put all the ingredients in a saucepan, over a medium heat, and reduce until the syrup is thick. Drain through a sieve, once cooled, refrigerate until ready to use.
Dry shake! Put 2 egg whites in the shaker and shake well. At least 30 seconds!
Now add the gin, syrup, and the lemon juice. Add ice cubes and shake for a long time.
Pour into 2 glasses and fill up with soda water. The egg white foam will float on top.
Using the zester, grate some fresh lemon zest over the top and decorate with the mint.