When I was in culinary school, I worked at a Mexican restaurant called Casa del Sol (Spanish for Casa "of" Sol). I was a line cook, but on weekends the owner let me get some extra hours working behind the bar on the restaurants outdoor patio (you can see the umbrella in the old photo below).
I didn’t have any bartending experience, but luckily 95% of the orders were for beer, simple mixed drinks, and the Casa del Sol's famous margarita. The food was very, very good - the owner had actually sent the chef down to Mexico for a month before opening to taste the real thing - but, the restaurant's claim to fame was its perfectly concocted margarita.
Like many bars that feature the margarita as the signature drink, the recipe was a secret. Not only was the recipe a secret, but the owner, Harry Tucker, would make the mixture across the street in his home, and carry over a bucket to the bar when needed.
It was quite a show (done intentionally, no doubt) - we would "run out" of margarita mix, and everyone would sit, wait, and watch, as the mix-master himself walked across the street to return a few minutes later with a 5-gallon bucket of his secret potion. Sloppy clapping and drunken hoots of joy would fill the air. Good times.
Here is my "secret recipe" for margaritas, presented in a video recipe I recently did for About.com. Remember, I can't embed the video, so when you click on the video, a new window will open. Enjoy!
Casa del Sol Photo (c) bunksplace.com