Ingredients: 1 1/2 oz white rum, 1 tsp sugar, 1/2 oz lime juice, 1 cup crushed ice. Put in a blender and blend until “frappéd”, whatever that means.
Source: The Unofficial Mad Men Cookbook
In the fifties and sixties, liquor companies like Bacardi used cocktail recipes to promote their product. Mad Men highlights this by showing Peggy coming up with a frappé recipe for a Bacardi ad campaign.
I am not a fan of iced drinks like this. NOT A FAN. But if you like to drink slushies have at it.