About Town Cocktail Book by Joe Fitchett (1925, p.18) — Shaughnessy Golf Club

1 measure per persongin base
1 lemonlemon juice — Juice of one lemonbase
0.5 measure per personcream — Add cream last.other
2 tablespoonfulsConfectioner's sugar sweetener
  1. Shake the lemon juice and sugar with ice.
  2. Add gin and shake again, then add cream last and shake well.

Ice: Ice

This matters because it preserves a club favorite cream-finished gin sour in a social source rather than a strict bar manual.

The source explicitly warns to add the cream last.

See also: Gin Sour, Dream Cocktail