I finally found some Austrian apricot eau-de-vie. Good and expensive but worth it. I tried this with the eau-de-vie instead of the apricot liqueur and the other Pendennis Club (I believe the 1939 Baker recipe that calls for "dry apricot brandy"). They are both sublime. I love a cold, dry cocktail, and these fit the bill.

I halved the apricot liqueur and enjoyed it more: an improved martini really.

I found this to be exceptional. Had it as an evening sipper. Did find it slightly sweeter than most of my evening cocktails, but very enjoyable. This is a cocktail which the quality of your gin will impact the final result. I used a gin which is softer and a bit sweeter. Would use a more assertive gin next time.