La Bodeguita del Medio is probably Cuba's most famous bar and restaurant. The mojito's popularity soared when Hemingway proclaimed that his mojitos were from La Bodeguita as well as "El Floridita" soared when Hemingway proclaimed that his daiquiris where from that bar. in El Floridita there is even a statue of Hemingway sitting at the bar drinking a Daiquiri.
The authentic mojito récipe is printed in the Bodeguita menú and even though your spanish is probably better than my english I translated it anyway:
In a (tall) 8 oz glass
1/2 tsp of sugar and 1/2 oz lime juice
Add spermint leaves and 3oz of soda wáter smash the stalk (without damaging the leaves)
Add 2 or 3 ice cubes and add 1 1/2 oz White Rum (Havana Club 3 yrs if you can get it)
Stir and enjoy
Although is debatable wether it is the best mojito in Havana there is no doubt that it is the most popular and famous.