make sure the ice is about twenty degrees below zero (centigrade). Don’t take anything out until your friends arrive; then pour a few drops of Noilly Prat and half a demitasse spoon of Angostura bitters over the ice. Stir it, then pour it out, keeping only the ice, which retains a faint taste of both. Then pour straight gin over the ice, stir it again, and serve.

https://www.bfi.org.uk/features/discreet-charm-perfect-martini