1. Prepare and ice-water bath; set aside. Bring 4 cups water and salt to a boil in a medium saucepan. Add mint leaves and cook 10 to 15 seconds. Drain, and immediately transfer to ice-water bath to cool. Drain and squeeze dry.

2. Place half of the mint leaves in the jar of a blender with enough oil to cover; blend for 2 minutes. Add remaining leaves and oil and blend for 2 minutes more. Transfer to an airtight container and refrigerate overnight.

3. Strain mint oil through cheesecloth and discard solids. Oil can be kept in an airtight container, refrigerated, for up to 5 days.