Hi ! Citric acid powder works fine for me, just make sure to dissolve it in a tablespoon of water first. You could also add lemon juice, but that would make the cocktail 'blurry' (and you would need more of it). Cheers !

Although a fan of Amer Picon in cocktails, I found this one a bit 'flat' at first. Added a knife's tip of citric acid dissolved in 2 tablespoons of water and 2 drops of 4:1 saline solution and that made a good cocktail a great cocktail (to my taste).

Tried this one (twice!) with different Calvados and Blue Curacao as I ran out of Orange. Besides the fact that the final color now looks as if this drink was made in Tchernobyl, this really IS a revelation.

Choice of Calvados however made a huge difference. I tried one with a Boulard Calvados VSOP, which makes for a more full bodied but less 'sweet apple'-taste, whereas a 'simple' 2 yr casked Calvados gave this cocktail a lighter, fresher taste.
Both were however very pleasant!

During my travels in Vietnam, I asked for a different version in - as I remember correctly - in 2 Lam son bar in Saigon (Hyatt hotels).

As I am a afficionado of (dry)martinis, this version included both dry vermouth and Gin on my request and had the following mesures : 4 cl London Dry Gin, 2 cl Dry Vermouth ( I think it was Dolin), 1 cl Midori, 2 cl Cointreau, 1 cl Lime juice.

The Vermouth brought down the sweetness of the Midori and added depth, where the Gin added stiffness.

This is probably a totally different cocktail then a Japanese slipper, but I liked it !