How to Make It
Bring a small pot of water to a boil over high. Add basil; cook until bright green, about 20 seconds. Immediately transfer basil to an ice bath; submerge until chilled, about 1 minute.
Transfer basil to paper towels, and gently squeeze dry. Process basil, oil, zest, and salt in a blender on HIGH until basil is very finely chopped, about 1 minute. Pour mixture through a cheesecloth-lined fine mesh strainer into a bowl; let strain, stirring mixture occasionally, about 5 minutes. Press on mixture to release additional oil; discard solids.
Store oil, covered, up to 3 days. To use, drizzle over soups, use as a vinaigrette base, or stir into pasta.