Freezing basil is a great way to preserve its deep, unique flavor to enjoy in the depths of winter when its taste brings to mind happy thoughts of summer gardens.
Unlike other green herbs which suffer little from freezing, basil requires one extra step if you want it to emerge from the freezer as green as it was when it went in: blanching. Simply bring a pot of water to a boil, dip the basil leaves in for 30 seconds, drain the basil, and squeeze out as much liquid as you can (rolling it in a clean kitchen towel does a lovely job, but so, too, do a pair of strong hands).
At this point you can simply double-bag the basil, pushing out as much air from the bags as possible, and pop it in the freezer. I prefer, however, to whirl the basil in a blender with a bit of olive oil to make a thick puree. Freeze this in small covered containers or in a clean ice cube tray (once frozen through, transfer the basil cubes to a sealable plastic bag for long-term storage).
If your favorite way to use basil is in pesto - go ahead and make the pesto when the basil is fresh and freeze the pesto itself. You'll be glad you did on the snowy/rainy night in November when traffic getting home is a bear and you're in need of a delicious but extremely easy dinner!