Now that I have W&N Overproof, I tried Andrew Willett's formula:
1 3/4 oz Wray & Nephew White Overproof
1/4 oz Curacao or triple-sec
1/2 oz key lime juice (freshly-pressed)
3/4 oz orgeat
I used Cointreau for the Curacao/triple-sec, and I had to substitute ordinary Persian lime juice for the key lime juice. I did go searching for key limes but I rarely see them here.
Willett's instructions are to shake the drink with method ice, not crushed ice, then double strain into a glass with service ice. Forgive me that I am not familiar with barperson's terms. For the method ice I used little tiny cubes from my Japanese Kotobuki ice trays, and for the service ice I used regular cubes from Rubbermaid. I hope this was the general idea.
What was unexpected is the level filled only about a third of the glass. I think I need trays for bigger ice cubes. Willet calls for only two cubes, and two was not enough. One nice thing is that most of my attempts have ended up too diluted by the end, and this technique holds up better.
Willett asserts this recipe is "at least as original as anyone can prove". And I agree, it works. I'm going to try reducing the orgeat to 1/2 oz and see what happens. Wish me luck.