Commercially available barley malt syrup is optimized for baking, not stirring, so to make it work in this drink I heat a bit of it in water on the stove until the color and flavor have mixed in. Malta sodas, such as Goya and India, have a similar flavor and can be substituted, but be careful as they are both very sweet and overwhelmingly flavorful. You want the barley to accent the whiskey, not engulf it.

A less expensive Mezcal may certainly be used, but don't skimp!

Now that sherry is relatively well understood and publicized, more contemporary cocktail menus should experiment with Madeira, which comes in a similarly broad range of flavors and textures from the brightly acidic Sercial to the PX-like richness of a Malvasia/Malmsey. Unfortunately there's the matter of price...

The original was an exercise in simplicity, a sour made simply of Drambuie and lemon, with optional bitters and orange flower water. The new version is a Rusty Nail Sour with flowery bells and orange whistles.