I feel like shaking the cocktail has made it loose it's 'body' a bit, leaving a rather sugary flat taste. Will try again but stirred instead of shaken.

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!