This drink was created by the Blue Blazer's Gerbert "Shorty" Doebber in 1952 for two oilmen who were regulars, Smith and Curran. Over the years the drink was distorted from it's original ingredients and name.
The bar atmosphere in which it was often ordered caused the name Curran to be misheard as Kearns and the original creme de cacao was soon replaced with Kahlua, or coffee liqueur. Both versions are great, personally cacao is my favorite, but if you order it in a bar you will probably get coffee.
This drink is often also served by without shaking or stirring, but in layers. Pour the liqueur into a glass with ice, add cream and top with club soda.
If you add vodka to this drink you will have a Smith & Wesson.