Blanching tender herbs before blending them in this versatile syrup preserves their delicate, fresh flavors. Use this refreshing syrup in cocktails or mocktails, or drizzle it over fruity desserts.
Bring a large pot of water to a boil over high. Arrange a double layer of cheesecloth in a strainer, and place strainer over a medium bowl so that strainer rests a few inches above bottom of bowl; set aside. Prepare an ice bath by filling a large bowl with ice water.
Add herbs to boiling water; cook, stirring constantly, 10 to 15 seconds. Using a slotted spoon, transfer blanched herbs to ice bath. Let cool 5 minutes. Drain, gently squeezing out excess liquid, and transfer herbs to a blender. Add simple syrup to blender. Process on high speed until herb mixture is smooth, about 2 minutes. Pour into prepared strainer, and let stand, stirring occasionally without pressing on solids, until all liquid has passed through strainer, about 1 hour. Discard solids.
Herb simple syrup may be stored in an airtight container in refrigerator up to 1 week.