We enjoy this one a lot, with a couple of tweaks to dry it out further. No sugar as Simon suggests, instead upping the whiskey to 7.5 mls for a little sweetness. The fragrance of the cucumber slice is key.
I'm sipping one of these right now. Didn't have any Japanese whisky, so I used a Highland single malt. I quite like it, but next time I think a touch more vermouth, and lose the simple. It's already sweet from the whisky.