Stir with ice, strain into a chilled cocktail glass.
This is an interesting vintage cocktail, altered only due to the lack of rowanberry (mountain ash berries.) Cranberry juice cocktail seems a reasonable substitute for what was likely an equally sweetened version of rowanberry juice. Rowanberry is otherwise quite tart from what I understand--similar to cranberries.
The original recipe calls for San Silvestro which was a Centerbe made by Aurum, appears to be no longer available although Aurum orange liqueur is. I used Faccia Brutto Centerbe.
I would be interested to hear how actual rowanberry juice works in this drink. I don't have a source for the berries, but I found that cranberry juice made a good libation. It was only slightly sweet, and quite potent.
I have also tried this as 1.75 gin: 3/4 cranberry juice: 1/2 Centerbe, which was also good.
Per the 1937 UKBG, this cocktail was created by Leslie Shelley at the Berkeley Hotel in Knightsbridge, London using rowanberry (sweetened juice?)
1937 UK Bartender's Guild Approved Cocktails