Basically, a rum and coke with a squeeze of lime, but Cuba Libre has much more of a ring about it. Zesty lime and dashes of bitters add layers of complexity...
From all the research I have done, I have never, ever, seen a Cuba Libre recipe which calls for Angostura, and generally, the proportions for rum to coke are more towards 1:3 (according to the International Bartender's Association, it's 5cl rum and 12cl coke) but of course, this is a matter of preference. Also, there is no muddling in a cuba libre, you just add 1cl of lime juice.
Now, I don't know who adds these recipes, but why is Angostura listed?
I'd venture to say it's to further cut the sweetness of the cocktail in general, and to hew towards the standard that says it's only a mixed drink w/o the bitters, i.e. not a cocktail, strictly speaking.
Yes, the classic recipe calls for just "Rum, Cola and Lime". But a single dash of Angostura bitters adds a much welcome layer of complexity to it if using light rum. Though I don't find it particularly necessary if using Havana Club Especial or Bacardi 4 años for example.
I'm not a big fan (correction: I'm no fan at all) of coca cola, but having bought a bottle of Fever-Tree Cola it seemed only right to try some sort of Cuba Libre. I've also got a bottle of Wray & Nephew rum which, at 63%vol would mean I'd not be in any fit state to complain if the drink disappointed. As it happened, I'm feeling very warm and fuzzy and almost (almost!) tempted to try this again with a gen-you-wine bottle of Coke. I do think the Wray & Nephew is a killer spirit - try it!
Tried this again, but using Coke from Mexico. There is a difference in the taste. Also used 1/24 oz (thank to Simon's wonderful jigger) of Pimento Dram instead of the bitters. Was wonderful.
I have been drinking Cuba Libres for nearly 50 years, this is the best cocktail recipe I have found. In Mexico, there is just a hint of lime, but the Coke in Mexico is different what is sold here in the US (I do use the sugar only Coke). In Mexico the Coke is also made with sugar only, but there is a hint of vanilla. This is great with either brand of Coke.