From recipezaar.com. Also works well with other herbs, like parsley,
dill, or cilantro.
2 cups fresh basil leaves, packed
½ cup olive oil
Puree basil in the food processor. Slowly add one half cup olive oil until
the mixture has the consistency of a smooth paste. Pour the puree
into plastic ice cube trays. It's best to have a special tray just for
herbs, because the remaining flavor will then get into your ice cubes.
Cover with plastic wrap, and freeze until solid. Store cubes,
double-bagged, in the freezer and add to soups, salad dressings, and
sauces for an instant flavor boost.