While the Mint Julep is a very old, classic drink, going back to the beginning of the 1800's, the term "Julep" is downright ancient dating back to about 600 AD. It was a word that essentially meant "Medicine", much like "Tonic" but there's obviously no medicine in the Mint Julep (or any julep for that matter) so what gives? Well, ancient people (And even not so ancient people) had a funny idea of what "Medicine" entailed and at least when possible it involved booze. The modern Julep of course was never intended as a curative, the name it seems is something of a joke. Similar to when my Grandmother would request her "Nerve Medicine" or her "Tonic" what she meant was "My bottle of blackberry brandy, no glass please".
The Mint Julep itself has a long history and has seen much evolution in it's standard preparation. Brandy, Cognac, Rye, Bourbon, even Rum have all been featured in it's silver beaker. Syrup or sugar, and which sugar? Bitters? Of course yes, all of these have at various times been considered standards in the Mint Julep. For what it's worth I prefer Bourbon in mine, made with a bit of demerara syrup and some bitters, and plenty of mint.
Like any drink with so much history, the Mint Julep has found itself regarded as a matter of religion among it's devotees. Many insist that you must not muddle the mint, or on the number of mint leaves to be utilized, on the amount of time the drink must rest, on the quality of ice, etc. Much like the Old Fashioned, a great many people have some very strong ideas about how it must be made.
Personally, I don't have time for that. I like my mint muddled here because I was the drink to be quite minty, but if you prefer not, that's no skin off my nose. The only things of true importance in my opinion here are that liqour, copious ice, and great quantities of mint are involved. My preparation is as follows:
~.5 oz. -or- ~ 15 ml. Simple Syrup
2 Dashes Angostura Bitters
A plethora of mint leaves
3 oz. -or- 90 ml. Bourbon
Fill beaker partway with crushed ice
Top it up with ice
add a bouquet of several sprigs of mint