2 ounces gin
3/4 ounce Rose's lime juice
Shake with ice. Strain into an ice-filled old fashioned glass.

There are very few times when I recommend the use of a "commercial mix" when making cocktails. The Gimlet is perhaps my only exception. This drink was most likely first created as a way to utilize Rose's Lime juice/cordial, and frankly it isn't quite the same thing if you attempt to use fresh lime juice and simple syrup instead.