Harry of Ciro's Princess Mary Cocktail combines gin, creme de cacao, and fresh cream.
Harry of Ciro's ABC of Mixing Cocktails by Harry of Ciro's (1923, p.69) — Harry of Ciro's 1923
| 0.5 glass | gin | base |
| 0.5 glass | creme de cacao — Creme de Cacao | modifier |
| 0.5 glass | cream — Fresh Cream | other |
This matters because it preserves an explicitly dated royal-name cream cocktail in the London 1923 field.
The equal three-part creamy structure is the main source feature.
L'Art du Shaker by Dominique Migliorero (1925, p.53)
| 0.33 part | gin — Gin | base |
| 0.33 part | creme de cacao — Creme de cacao | modifier |
| 0.33 part | cream — Fresh cream | other |
The source attributes this to Harry McElhone of the New York Bar, Paris.
Barflies and Cocktails by Harry McElhone and Wynn (1927, p.62) — Wedding 1922 note
| 0.33 part | gin | base |
| 0.33 part | Fresh cream — Fresh Cream | dilution |
| 0.33 part | creme de cacao — Creme de Cacao | modifier |
This matters because McElhone explicitly ties the drink to Princess Mary's 1922 wedding, giving it a useful interwar social anchor.
See also: Alexander Cocktail, Milk Punch