For my taste, this is too sweet. Re-mixed it with 1/4 oz/7.5 ml rich syrup and it was more enjoyable. The Bourbon was more prevalent at that ratio.
For those commenting that it was too minty, a "julep" has mint as a predominant flavor. Something you can try, instead of muddling the mint leaves, is to just add them to the shaker without muddling. As you are shaking the cocktail, the ice will bruise the mint leaves just enough to give the cocktail a more subtle mint flavor.
Do not overdo the mint like I just did. Used 8 big leaves and let it sit in the tin with the bourbon too long while looking for my strainer. Ended up way too minty, pretty much the flavour of mouthwash.
For those commenting that it was too minty, a "julep" has mint as a predominant flavor. Something you can try, instead of muddling the mint leaves, is to just add them to the shaker without muddling. As you are shaking the cocktail, the ice will bruise the mint leaves just enough to give the cocktail a more subtle mint flavor.