Our favourite version of this substitutes Del Maguey Crema de Mezcal for the Tequila. Since the Crema has roast Agave syrup as a component, we go with just 5ml sugar syrup. Dial the Crema back to 40-50ml if 60ml Mezcal seems excessive. The Mezcal gives as good as it takes up against the ginger beer. Delicious.
I’ve made this several times now. It’s definitely a go-to. After experimenting I now use agave syrup instead of sugar syrup. Last couple I’ve also been adding a half ounce of a locally(BC, Canada) produced quadruple sec with enjoyable results.
To be honest, the pic above is so old that it's pre-digital so I suspect the colour difference is due to our bad image rather than a difference in ginger beer. Fever-Tree does have a good bite to its ginger beer.