Thank you John Hinojos for your tip. I used Calvados, Laird's Applejack and Triple Sec as mentioned. Added 1/2 shot of Apfelkorn (a 20% german apple-liquer) and no water. This cocktail was a succes. FINALLY, If you serve two of these, remind your guest to stay seated for a while.
We tried this one the next night but used 2 parts calvados to 1 part applejack bottled-in-bond (100 proof). Citrus flavour is less pronounced and the taste of the apple brandy is stronger. Both are good, but I think I would stay with the one with the 100 proof. Has more depth of flavour.
What an outstanding apple flavoured cocktail. Although I have 2 different Calvados, decided to use Laird's 86 for a little extra proof. Nicely dry with the great citrus-apple flavours. May try next with just a little Applejack bottled-in-bond for little extra kick. In my favourites.
As I have no Apple Schnapps Liqueur I had to balance on an other way. The "Tarte Tatin" from the older comment made me try a dash of vanilla syrup, honey and saline solution. The result is good, but not very special. Let's call it "Apple Tart" ?