I am going to give this recipe a try with a rosemary tincture in lieu of substituting gin to 'beef' it up. Haha, but a London dry would be all wrong anyway. I would consider dumping some Hendricks or an Old Tom in there but any gin is going to overpower the subtle notes of the Aperol and StG's. a tincture is pretty harsh too but a few drops of one seasoned with rosemary should do just the trick.
I will try small versions all three ways and proffer some reflections.
I tried the original recipe in a half portion and it was way too sweet and sour in alternating doses.
I used an ounce of Hendricks (half ounce) on the variation and found it to be a delightful drink. However, it was similar to a Negroni with more sweet and less bitter in the aftertaste (this is obviously discounting the tones of rosemary that make is markedly different in aroma). The real problem was this: the drink didn't taste much like a 'sour' anymore with the gin. It was a good drink but an entirely different one.
Using the half measures again, I made a version and used sweetened lime juice (in lieu of fresh squeezed in the others) and 2 ml of rosemary tincture and no garnish. It was easily the best of the three and still had a flavoring in keeping with the drink's name. The sweetened lime juice gave it that nice 'sour' feel and fortified the mixture against the introduction of 50-60% alcohol tincture (I used equal parts water and everclear for the recipe).
Finally, I celebrated my tweak with a regular sized version:
1 1/2 oz Aperol
3/4 oz St. Germain
3/4 oz Rose's Sweetened Lime
3 ML of Rosemary Tincture
shaken well in ice and strained into a chilled coup then garnished with a small sprig of rosemary (no need to slap). It was fantastic and I will be making this for friends soon enough to get their thoughts.